I don’t know how relevant this is to you but I was looking at getting a Boox since it would easily let me read my Kindle and Kobo books on a single device without any hassle. However, it achieves this by running their apps so the books are segregated. There’s no one library with all your books. Your Kindle books are only on the Kindle app, your Kobo books are only on the Kobo app, your library books are only on the Libby app.
It sounded really tedious to have to flip between a bunch of different apps to track all my books so I decided to just stick with Kobo.