Haha, I just came to the same conclusion. I was told the same thing back in 2016. But of course, after 2 new phones, I forgot all about this feature ...
And strange enough on Android, I now can zoom in. The title and author + meta data is all in CC Companion. Then I choose to open in FBReader and I see the title and author, but the manual added comments are missing in FBReader.
I did a test (scenario 5) on iPad. I installed KyBook and manage to connect to Calibre, browse all books, see all meta data. I download the eBooks, and all meta data is copied KyBook.
So it looks like this is a FBReader issue... or am I missing something ?
Thanks @stumped for the help