Thanks, I'll have to check out the Fire, then!
The Moon+ backup files are "hidden" zip archives, that contain (among other stuff) database files with the reading statistics Moon+ stores for each of your books. I wrote a quick Python script that reads these statistics from all my backup files, aggregates them, and generates a visualization. If you're interested, I'm planning to put it on Github so that everybody can use it when I'm happy with it. Here's an example:
https://erlenddahl.net/etc/books/ (looks very ugly on tiny screens yet, so I recommend using a computer).