Books

I got a Boox Nova Air and it has some trade offs. None of the ereaders are open source/Stallman-esque ethics friendly really but I do like that with Android based readers like Onyx Boox you can read in whatever app you want (like I had some purchased on Kindle, Kobo or even the Libby library app or Scribd subscription service.) This works for me since I can have those multiple sources. However, I found the Kobo Libra H20 to be a more polished and enjoyable experience so if all you're doing is putting files on and not worrying about having multiple source access then I'd recommend that form factor.