My last eReader purchase was the Kobo Clara 2E and it’s fantastic. I got one for my dad as well. I love the fact that you can use it completely offline and without any account.
Then they announced a partnership with IFixIt, and that cemented for me (barring any changes), that my next eReader will also be another Kobo… though with this partnership I expect that to be a long time down the road.
Not without significant hurdles due to Amazon’s (very intentionally crafted) walled garden. You’re locked in by the file format as well as Amazon’s DRM. If you do anything to bypass this, it’s technically illegal as a violation of the DMCA.
Did they make this easier? I have a Sage and I had to open a SQLite database file on the e-reader, then flip some flag, to bypass account sign in. But that was a few years ago.