I've been a happy Calibre user for years, and have steered many people in that direction. I particularly liked the fact that I was no longer limited to ONE device for my books. Amazon is so weird about ebooks that we BUY. I loved the feature that allowed me to import the books to Calibre and then I could group by genre or author or what-have-you.
My problem is this. My desktop computer died. OK, I got a new laptop and tried to set it up so that I could RE-download my books and I would have them again. Nope. First, Amazon no longer allows you to have Kindle for PC associated with a business account. You have to have a REGULAR account, and then link the business account, and you could 'share' the books within the family. Fine.
I get Kindle for PC installed and find out that I can't use Calibre with it, because it is the newest version of Kindle for PC and they are incompatible. Fine. I fix that. Now, I find that Calibre can no longer import and convert the Kindle ebooks. WHAT?? It worked on my desktop 3 days ago.
WHAT CHANGED??