Given this multi-file format headache for dealing with liberated books that you sideload into the Azon system....

..Do some users who similar to HarryT aren't concerned about the proprietary file formats, just go all the way and use everything in its 'native' Azon DRM'd state, to avoid all the format/conversion/sideload hassles? And then just liberate and keep copies of their purchased DeDRM'd ebooks in Calibre for archive and future-proofing purposes?

I don't plan to do that myself, but I could see that approach could make sense for some people. If you're not concerned about the proprietary lock-in situation, this approach would give you all the Azon functionality in reading, reduce file format hassle and hassle syncing across devices, but still gives you a future-proof library.