An e-reader with an app store promises Kindle, Kobo, Libby and your own files on one screen, which sounds like the end of a familiar frustration. XTEINK, a small Chinese maker of readers that snap magnetically to the back of a phone, has added an Android model, the S4. In practice it’s more mixed than that, and it depends on four specifications that marketing pages rarely lead with.
The S4’s listed specs
XTEINK calls the S4 its full-featured reader, built for mainstream reading apps with no lock-in to one store. It’s the first model on the maker’s website to run Android. The X3 and X4 use the company’s own firmware, which XTEINK flashes through a browser tool on the same site.
The S4’s hardware is modest: a 4.3-inch E Ink touch screen, physical page keys and a front light with adjustable warmth. XTEINK lists it at 6.98 mm thick and about 95 g. Its 32 GB of internal storage is shared with the operating system, and there’s no microSD slot. It has 2 GB of RAM. The Android version is 11, which Google released in September 2020.
Where it is on sale
XTEINK shows the S4 on its Chinese website. On October 18, 2026, its English-language store was selling the X3 and X4 models, and the S4 wasn’t among them.
For a small brand, an export listing can follow a domestic launch by weeks or never arrive at all. If you’re outside China, treat the S4 as an import until it appears in the international store. That means no local warranty and slow support.
Android and E Ink pull against each other
A closed reader ties you to one bookstore. Someone who borrows library books and has a Kobo, a Kindle account and a stack of side-loaded PDFs has good reason to want something more open.
Android was written for screens that redraw themselves dozens of times a second, and E Ink doesn’t work that way. The screen holds an image with no power and changes it by moving charged pigment particles through a fluid. That physics gives you daylight readability and weeks of standby. It also turns every animation the operating system takes for granted into a problem the e-reader has to work around.
Full and partial refreshes
An E Ink panel can update in two ways. A full refresh rewrites the whole screen, usually flashing it dark and then light, and clears leftover traces cleanly. A partial refresh changes only the region that moved. It’s far quicker but leaves faint remnants of the previous image behind. Those remnants are called ghosting.
A purpose-built reading app turns pages, so it can ask for a full refresh at sensible intervals and accept the flash. A general Android app scrolls, fades and slides panels in from the side, and on an E Ink panel each of those becomes a smear.
So the quality of any Android e-reader depends less on the app store than on the refresh-control layer the maker builds on top of Android. When you look at one, check whether you can set refresh behavior per app and how many modes there are. Makers who have been doing this for over a decade generally provide that, and a first attempt often doesn’t.
Why memory matters more here
The firmware on a closed reader renders EPUB files and little else. It needs very little memory, so 512 MB of RAM can be plenty.
On Android, the operating system itself sits in memory, and so does the launcher. Your reading app, a bookstore app and a sync service sit on top of that. With 2 GB of RAM, switching between two reading apps often means the one you return to gets rebuilt from scratch. On a screen that redraws slowly, you watch that rebuild happen.
A storage figure like 32 GB is shared with Android and its cache, so you get less usable space than the label says. Without a card slot, that number is also final.
The Android version and app support
Buyers skip this specification more often than any other. An e-reader that ships on an old Android release inherits whatever app support that release has left.
Android 11 arrived in September 2020, so a reader shipping on it in late 2026 starts six years behind. Reading apps rarely drop old versions quickly, and many will keep working for years. Even so, the pool of apps that still install only shrinks, a little more each year. A closed reader ages differently, because one company maintains its bookstore and its firmware together.
What open Android buys you
Android lets you run the reading app you already pay for and keep one library across devices. You can borrow from a public library through whichever app your library supports, and use a third-party reader for formats the built-in software refuses.
You also get text-to-speech, a browser for saving articles and, on larger models, note-syncing services. A locked reader has none of that at any price.
The cost is that you assemble it yourself. Nothing is wired together for you, and you become the person who maintains it.
Judging one before you buy
Four checks cover most of the risk. Look for refresh modes you can set app by app, and for at least 4 GB of RAM if you plan to run more than one reading app. See whether storage can be expanded, because without a card slot the internal figure is the ceiling. Check the Android version too, and treat anything several releases old as a countdown.
An established maker’s take on the same idea makes a useful comparison. The BOOX Go 7 is a seven-inch reader built around this trade-off, with a full Android build, an app store, a card slot and text-to-speech. It shows what the mature version of the concept looks like and what it costs.
Who should skip an Android e-reader
If you read novels bought from one store and nothing else, an Android reader adds complexity you’ll never use. A closed reader will be faster and cheaper, and it’ll ask less of your attention.
Anyone who juggles library loans, PDFs and two different bookstores will find the openness pays for itself. Buy it on the four specifications above. The app store is the easy part, and the refresh layer decides whether you enjoy using it.
