I'd recommend the Remarkable 2 tablet. Runs Linux, active hacker community, gorgeous epaper display.
Sony makes a nice one as well, but it's a lot more expensive and a lot more locked down.
These Waveshare displays are more suitable for Arduino projects.
and Sony recently decided to stop development of new models.
Do you have one? From what I've seen people seem to think the hardware is solid but the software is rather lacking.
I recently bought a Boox Note 2 for this and it works very well. I had previously tried reading PDFs and technical documents on my Kindle but it was pointless since it was so small. The Note 2 is just a little smaller than regular letter size paper and it runs a full Android operating system so it's easy to get whatever document management system you want to use working on it (including the Kindle app).