I REALLY don’t agree with giving Amazon money (ethically) but I am a hypocrite and end up buying a lot of ebooks and audiobooks from them, I do my best to back up the files using calibre but I‘m sure they could lock down devices / files using DRM and their latest DRM incarnation is very hard to remove. I try to buy DRM-free ebooks and audiobooks whenever possible but I think mostly due to market domination authors and publishers end up at least mostly exclusively providing content via Amazon.