Readers like you help support Android Police. When you make a purchase using links on our site, we may earn an affiliate commission. Read More.

Onyx is continuing its crusade in the name of e-reading, though it might be more appropriate to call its devices E Ink Android tablets, as they don't come running locked down operating systems like Amazon's Kindle e-readers or reMarkable's tablets. One of the latest models from Onyx is the Boox Tab Ultra C, and it puts a colorful spin on the Boox Tab Ultra we reviewed in March, which is already an appealing device.

I've used a number of Onyx's earlier tablets, including the big-screen Boox Note Air and the colorful Boox Nova Air C. The Boox Tab Ultra C is effectively bringing the best of Onyx's various product lines with the powerful hardware that comes with the "Ultra" name. There are some trade-offs to brightness for black-and-white content with the addition of the color layer, but what color adds to just about everything outside of documents is easily worth the sacrifice.

While an E Ink tablet won't offer an appropriate display for everyone, the Onyx Boox Tab Ultra C is easily one of the most capable e-readers I've come across. For anyone looking to get a little further from the bright, eye-straining displays of typical tablets and laptops, the Onyx Boox Tab Ultra C and its color E Ink screen have a lot to offer.

BOOX Tab Ultra C review product box image
Source: Boox
Onyx Boox Tab Ultra C
8.5 / 10

The Boox Tab Ultra C makes a small sacrifice to brightness to deliver the huge addition that color brings to a screen. It succeeds in making a great e-reader into an even better one without adding much to the price tag. It won’t be for everyone, but the Boox Tab Ultra C has a lot of promise for eye-aching tablet users and comic book readers alike. 

2480×1860 (B&W), 1240 x 930 (Color)
128GB, microSD up to 2 TB
Screen Size
E Ink Kaleido 3 Carta 1200, 10.3 inches, 4096 colors
8-core, 2GHz
2 speakers, 2 microphones
Supported formats
Android 11
Wi-Fi 802.11ac, Bluetooth 5.0
Front light
Moon Light 2
225 × 184.5 × 6.7 mm
USB Type-C with OTG support
  • The softness of E Ink with color on top
  • Google Play included out of the box
  • Capable note-taking and drawing with included stylus
  • Ample storage for files
  • Optional keyboard turns it into a writing machine
  • Some minor ghosting can show up
  • Keyboard not included and a little tight
  • Not lightning fast
  • Less suited to pure reading
  • Expensive

Price, availability, and accessories

Onyx Boox Tab Ultra C with detached accessories on a tablet

The Onyx Boox Tab Ultra C has a list price of $600 on Onyx's own website as well as on Amazon. The tablet includes Onyx's upgraded Boox Pen2 Pro, a USB-C cable, and a tool for opening the microSD card tray. Onyx offers a few bundles on its site that include a magnetic cover and extra stylus tips. The tablet works with a special magnetic keyboard cover that adds $110 to the price but extends the functionality of the tablet considerably, making for faster web browsing and smooth document writing most e-readers can't come close to offering.


Onyx Boox Tab Ultra C displaying an e-book

The Boox Tab Ultra C is effectively just a variant of the Boox Tab Ultra and, as such, has an almost identical hardware design to that tablet. So you can expect a similar flat-edged metal frame that feels robust and luxurious for an e-reader. The bezels around the display are fairly thick, and one side is extra thick, providing space so you can hold it like a book.

Though common e-readers might not include speakers, the Boox Tab Ultra C packs a stereo set that can come in handy for everything from audiobooks, podcasts, YouTube videos, or even VoIP calls.

One edge of the tablet contains a series of metal contacts to link up with pogo pins on the optional keyboard case. The tablet also uses strong magnets to establish a secure attachment to the case as well as to latch the included stylus firmly to the edge. The flat sides of the Boox Tab Ultra C provide a much better attachment surface than the curved edges of some of Onyx’s other tablets.

One edge includes a USB-C port near the corner, conveniently placed so the cable won’t stick out if plugged in while in use with the keyboard cover. A microSD card slot sits above that port. The power button is on the opposite side, and that’s it for ports and buttons on the tablet. Most control is handled through on-screen menus.

The Boox Tab Ultra C is a larger tablet than the typical e-reader. It lends itself more to reading and marking up PDFs and A4-size documents than just e-book files that can reshape and resize to fit neatly on just about any screen size.

Like the standard Ulta, the Boox Tab UItra C includes a camera on the back intended to scan documents. As a result, there’s a document scanner app pre-installed instead of a traditional camera app. Since the display can show color, it may feel a little bit like a camera, but it’s not worth using in that capacity.

While it isn’t included, Onyx’s special keyboard cover is a convenient extra. I added a Bluetooth keyboard and tablet stand to use with my Onyx Boox Note Air, but I find the keyboard cover for the Onyx Boox Tab Ultra C far more convenient as a protector, stand, and keyboard all in one. The keyboard is rather cramped at the edges, and the keys are squishy, so for extensive typing, I’d still go with a better Bluetooth keyboard, but for everyday browsing and some quick emails, the keyboard cover is pretty convenient.

Display and stylus

Writing on the Onyx Boox Tab Ultra C E Ink tablet with included stylus

The key differentiator of the Boox Tab Ultra C from run-of-the-mill Android tablets is its use of a 4:3 E Ink display. Rather than shining light out through colorful pixels to create an image, the E Ink layer has pigmented metal balls that flip around to show either black or white. These create the pixels, and they can sit as they are almost indefinitely without using more power.

This is effectively how every e-reader display works, though the Boox Tab Ultra C is using a high-quality display with a 2480 x 1860 resolution and 300ppi pixel density for black-and-white content. What sets the Boox Tab Ultra C apart from the standard Boox Tab Ultra is that it uses the new Kaleido 3 display, adding a 1240 x 920 color LCD layer above the E Ink layer.

The LCD layer dims the E Ink slightly, but the tablet includes front-lighting with adjustable color temperature, so the display can still appear plenty bright for all types of content in all viewing conditions. Since the E Ink only appears brighter when under bright conditions, you actually end up seeing better and saving battery when viewing the display in a bright room or out in the sun — effectively the opposite of a typical tablet or laptop.

Onyx Boox Tab Ultra C E Ink tablet next to Samsung Galaxy Tab S7 Plus and Onyx Boox Note Air with screen light settings at maximum
Lighting set to max

The new Kaleido 3 LCD layer is a clear-to-see upgrade on Kaleido Plus. Two years ago, I found the color layer of the Boox Nova3 Color a little grainy due to its low resolution, which amounted to just 100ppi, and that made the reduction to brightness a hard sell. But on the Boox Tab Ultra C, the color feels like a more natural addition on top of the rest of the content and measures in at 150ppi. Navigating apps, browsing the web, and reading comics are so much more pleasant and easy with the added color, so it's well worth the small loss of brightness.

Onyx has simplified its display controls, using a slider to adjust brightness and a second slider to control color temperature (Boox used to use separate sliders for the warm and cool lights). The E Ink Center provides quick control over the display’s refresh modes and a few special color controls. The process of adjusting color is a bit obtuse, but the tablet comes out looking perfectly serviceable for most content right out of the box. The various refresh rate modes are handy, allowing for clean page turns with no ghosting, extra fast motion at the cost of more ghosting, or something in the middle.

Onyx Boox Tab Ultra C E Ink tablet next to Samsung Galaxy Tab S7 Plus and Onyx Boox Note Air with screen light settings off or at lowest value
Lighting at minimum/off

I found the Balanced and Fast modes plenty smooth for casual browsing and writing without introducing much ghosting. Ultrafast is impressively smooth for an e-reader, and it’s even more surprising how quickly the screen wipes away the ghosting. Even at its fastest, the display still isn’t smooth enough to show video content well. It’s possible to watch videos and get most of what’s happening, but fast movements are lost. The final lightsaber battle of Star Wars Episode I probably has never looked better on an e-reader, but it’s stilted and a ghosty mess at times.

All of the quality of the display is topped off with its support for a stylus, which makes for precise input in black and white or color. The tablet is perfectly responsive to the stylus as well, making for quick markups and notetaking, much like writing on paper (albeit a little more frictionless because of the glass display). However, the stylus response is almost exclusive to Onyx’s first-party apps. Trying to doodle in an Android app like Google Keep came with so much latency that there was no way to effectively use it. Evernote, OneNote, and WPS Office have special support but are still not as seamless to scribble in as the built-in note app.


Onyx Boox Tab Ultra C E Ink tablet with Google Play app store open

More than its hardware, the best feature of Onyx’s e-readers has been the use of Android, and it’s gotten even better. While earlier Onyx tablets required some obnoxious workarounds to get Google Play up and running, the Onyx Boox Tab Ultra C comes with it installed and ready to go from the beginning. This means you can load up just about anything you might on any other Android app. For e-book reading, this is big, as you can install the Kindle app, Kobo app, and even whatever apps your public library might use, like Libby.

Thanks to the color of the display, you can even dive into comic book reading apps (or use the default reader app, which supports CBR files). While having just 4,096 colors leaves the Boox Tab Ultra C falling far short of the millions or even billions of colors standard tablets offer, it’s still enough color to get by and enjoy a comic book or graphic novel with a slightly less critical eye. The addition of color here also makes up for one of the bigger shortcomings of the colorless Boox Tab Ultra, which could struggle with third-party apps.

The Boox Tab Ultra C is running Android 11 still, and it has Onyx’s heavy customization (more or less necessary to work properly as an e-reader). It can feel a little foreign for everyday Android users, but it doesn’t take long to get used to.

Onyx’s own Notes app is fairly feature-rich and more than capable enough for a wide variety of note-taking styles, from scribbling on a blank canvas, writing on a musical staff, and writing on lined paper to doodling colorful artworks with pressure-sensitive input. Likewise, the built-in reader app covers a huge range of file formats, and is easy to get the basics. The apps go fairly deep, though, and some of the settings are not so intuitive. Of course, the beauty of the Boox Tab Ultra C is that you don’t have to rely on first-party apps because you can install the apps you prefer.

Performance and battery life

Onyx Boox Tab Ultra C E Ink Android tablet sitting on table

While the Boox Tab Ultra C can do the job of even the best Android tablets, it’s not exactly meant to carry the load of one all the time. It features an octa-core processor, Qualcomm’s Snapdragon 662, but don’t expect Snapdragon 8 Gen 2 performance or anything. Apps can take a second to launch, and the limited 4GB of RAM means you won’t necessarily get to jump right back to where you were in an app if you switch around a lot.

I found the tablet able to keep up decently with a browser running in split screen with Google Docs open on the other half of the screen, but even just running Geekbench 6’s CPU benchmark seemed to be more than the tablet really was up for. After 7 minutes, it still wasn’t halfway through the benchmark when the tablet went into sleep mode and canceled the benchmark. I wouldn’t describe it as sluggish, but it’s certainly not a high-paced work machine.

Onyx Boox Tab Ultra C E Ink tablet docked on keyboard case

High performance is often offset by low battery life, but that’s not an issue here thanks not only to that modest processor but also in large part to the display technology. The Boox Tab Ultra C barely uses its 6,300mAh battery. Not having to refresh a high-resolution screen 60 or more times a second, like a typical display, really conserves energy. In my two weeks of testing, browsing the web, reading comics, scribbling notes, and playing YouTube videos, I’ve only managed to drain the battery to 41%. A lot of this time was spent with the backlighting turned on. Turn the backlight off, and your battery life will stretch dramatically more.

The tablet doesn’t lose a lot of charge when it’s sleeping, so you don’t have to shut it down when you’re done. I left it set to turn off after an hour of inactivity during my testing, which is more than adequate for daily use.


Bigme inkNote Color review front sleep splash

At $600, the Boox Tab Ultra C runs into plenty of competition but not much in the color e-reader space. Bigme's InkNote Color+ is a near equivalent device that upgrades from last year's Bigme InkNote Color with perhaps a little more muscle under the hood, but it's $100 more expensive. And it doesn't appear to offer a keyboard case accessory that can turn it into a work machine.

The Amazon Kindle Scribe and ReMarkable 2 are both about half the price at $340 and $280, respectively, while still offering large displays and a solid writing experience, but both are far more locked down when it comes to software, and neither have any color in their screens. The standard Onyx Boox Tab Ultra would make a strong alternative to anyone who doesn't need the color, as they'll save $40 with current pricing and get a brighter black-and-white experience. But I'd argue that the color makes the Boox Tab Ultra C so much more versatile that it's easily worth the trade-off.

Perhaps the biggest danger the Boox Tab Ultra C faces is from the Apple iPad Pro at $800 or Samsung Galaxy Tab S8 at $700. Both will be far more capable for the vast majority of users thanks to their powerful internals and high-quality displays. But, they miss out on the easy viewing of e-ink, are much heavier, and are harder to read in direct sunlight.

Should you buy it?

Like many of Onyx’s high-end e-readers, the Boox Tab Ultra C won’t make sense for everyone. For general use, a normal tablet will be more versatile and a lot more affordable while providing plenty of performance. But, for anyone who’s dying to spend a little less time looking at a lit-up screen or watching their battery die a record pace out in the sunlight, the Boox Tab Ultra C has loads of promise. It truly excels in its niche.

As an e-reader, it’s exceptionally smooth and capable. As a tablet, it’s at least quick enough to make browsing and light productivity a reality. Pair that with the best qualities of E Ink and sprinkle a little color on top, which goes a long way, and you’ve got the makings for an excellent product.

BOOX Tab Ultra C review product box image
Source: Boox
Onyx Boox Tab Ultra C
8.5 / 10

Enjoy a powerful e-reader that adds a splash of color to your content, all while enjoying the freedom that comes with Android.