[BeetleB]

Kobo lets you install your own SW. There are open source reader SW for the Kobo, and they're better than Kobo's own reader.

[dredmorbius]

What reader(s) do you like / recommend?

I've used FBReader, PocketBook (who sell their own ebook readers as well apparently), the NeoReader (default Onyx software), and have some familiarity with Kindle.

PocketBook enables some (but insufficient) metadata editing. The NeoReader has an excellent UI/UX generally on BOOX devices, but has no management capability.

I tend to have a large number of documents on my devices (1,000s). Management is critical.