Chinese startup Xteink has introduced the X4 Pro, an ultra-compact e-reader slightly larger than a credit card. It is designed to be thin and light enough to attach to the back of a smartphone, targeting users who want to read briefly while on the move.

On July 21 local time, IT outlet Engadget reported that the X4 Pro is Xteink's latest e-reader, as the company has focused on ultra-compact devices and a distraction-free reading environment.

The device is 5.95 mm thick and weighs 72 grams. It has magnets built into the body so it can attach to the back of a smartphone. Xteink also highlights that its size is only slightly larger than a credit card, making it easy to carry in a pocket or small bag.

Xteink explained that it uses a thin frame so it can feel less burdensome than a typical power bank even when attached to a smartphone. It is effectively proposing a use case in which users detach it from their phone and start reading right away, rather than carrying a larger e-reader.

The X4 Pro is not only about its small size. It comes with a 4.3-inch touchscreen display. It also offers page-turn buttons and a circular home button, and supports an adjustable front light for reading at night.

Because the screen is small, it is better suited to reading short, text-focused e-books than viewing comics or graphic novels. Engadget described it as aimed at users who want to pull it from a pocket to read a chapter or two on the subway or while waiting, while avoiding distractions from social media alerts and apps.

There are limits to how it can be used for e-books. The X4 Pro supports only e-book files without digital rights management (DRM). Users can send files wirelessly through a Xteink app or transfer them directly using a USB cable.

Supported formats are DRM-free epub and mobi files. Most books bought on Kindle or borrowed through the e-library service Libby cannot be transferred. That can be a limiting factor for users who rely on major e-book platforms. After pairing with a smartphone, users can manage an e-book library in the dedicated app. It also offers features such as downloading wallpapers and adding custom fonts, and those tasks can also be done via a USB connection.

The hardware is also tuned for an ultra-compact design, and the battery capacity is 1,100 mAh, higher than some earlier products. To keep the 5.95 mm thickness, it does not include a USB-C port on the body. Charging requires the included magnetic charging adapter. Built-in storage is 16GB, expandable up to 256GB with a microSD card.

It is priced at $99. That is not much different even compared with the base model Amazon Kindle, but the X4 Pro differentiates itself on portability rather than screen size or a content ecosystem.

It appears suitable for users who value a size that can be pulled out and read anytime and anywhere, physical buttons and a reading experience free from smartphone notifications over the convenience of an e-book platform. Still, the lack of DRM support and the need to use a dedicated charging adapter are cited as key variables when deciding whether to buy it.