Love my Remarkable 2, but my main use case for an e-reader is reading in bed at night, and it just doesn't work for that (form factor and lack of backlight, though the newer ones do have a backlight).
However, for reading technical docs or workshop docs in daylight, it's great.
The Remarkable 2 has an e-ink display but is rather underpowered as an e-reader. It does have an SDK for building apps: https://developer.remarkable.com/documentation/sdk