I'm not that fond of eInk, having tried a PocketBook Verse e-reader (more open than a Kindle, has a microSD slot for my 70+GB fully DRM-free eBook collection) with a fairly grainy screen.

A recent article on HN convinced me to try the M5Stack Paper S3. Much nicer screen with 16-level grayscale touchscreen, microSD slot, ESP32-S3 with WiFi and Bluetooth, supports the Crosspoint Reader software. It's got a magnetic back but won't fit on the back of a Magsafe phone like the Xteink4 can. It's double the price, but well worth it.