I've never understood the hubbub. You can easily perfectly convert between the formats with any number of tools. I use Calibre and I've never had a problem with a converted document.
Kindles are actively walled to force customers into the amazon ecosystem.
I could just plug this sony e-reader to my PC and copy whatever I wanted to read. The e-ink panels have gotten substantially better but the experience is now objectively worse with Amazon and more expensive, most customers not don't realize what it could be.