Notably they don't display book covers for converted epubs in your library -- clearly hamstringing the conversion so folks aren't too tempted to rely on books from external sources.

The AZW3 proprietary format is not something I want to struggle with in my day-to-day -- if anything goes wrong, it's a rabbit hole of reverse engineering. I like copying media to my ereader using cables, because sometimes I don't have a solid internet connection or it just feels wasteful to send a bunch of big files over email (if I'm on a tethered or metered internet connection, just sending a couple dozen books is easily in the hundreds of megabytes up and down).

Kobos are a much friendlier ecosystem, and are what I recommend to all family members who don't want their device shackled by Amazon. Easy to hook up to local libraries to borrow books on the fly, easy to copy DRM-free ebooks from online stores.

I have a Boox tablet myself because I love notetaking in nonfiction books and hand writing my notes in work meetings and journals.