Started with Android 4 KitKat, stuck with Linux kernel 3.4 :)
5.4mm thickness, 3GB RAM (enough for 32-bit), 2TB SD card works, watching movies/shows with the AMOLED look as good as a recent OLED TV. Truly ahead of their time.
SDR content with mDNIe dynamic enabled comes surprisingly close to HDR content on an HDR display, colors can be a bit too staturated though.
After a decade, the battery lasts a week for daily hour e-book with black background. 3 hours of video playback. However, it restarts at 30% battery when running at full brightness with a white background. Disabling Wi-Fi significantly extends standby time compared to modern hardware.
Caveats: Slow web browsing and no H.265 hardware decoder. 1440p H.264 60Mbit is the max (Display is 1600p). Most content providers and streaming services are slowly moving away from AVC, so it's stuck at 720p H.265 on CPU.
Back in 2014, I couldn't have imagined using hardware that was over a decade old.