I got an Xteink X 4 a few weeks ago and it's a very cute device. While I'm a fan of the hardware what's been really fun is noodling around with building some custom firmware and sync architecture to optimize content for the device's extremely limited CPU and Memory. That's meant a custom format for images and metadata that match the device's hardware and interface needs and an automatic ingest pipeline for building these files from common book/comic formats. Maybe some day I'll even read a book on the thing!
It saddens me that most of the ebook world is leaning towards smaller screen sizes.
My reader is 8", and I think that's just the right size. I like a decent sized font, and I don't like continually scrolling.
Surprisingly, the original promise of "low battery use" isn't panning out. My ereader's battery doesn't last that long, although I can live with it. Once you switch to large size color eink screens, the battery life is poorer than tablets!