Hovering over icons: it works, sorry, it was my mistake.
Calibre is a Windows/Linux/Mac application. I'm on a Windows. Maybe it's just me, but I'd also prefer the less frequent but more substantial updates on a Linux or a Mac as well.
Calibre is more of a converter/manager program than an e-book reader, right? (I don't use the manager, I just need the converter, but maybe that's just me.)
As for Calibre as a reader, on the ebook-viewer.exe on the desktop I cannot use notes and bookmarks which are crucial for me for a proper reader app. On the other hand, it does have a dictionary integration which is cool.
I haven't tried the Calibre Companion for Android but it is also more of a manager, than a reader, as far as I understand, right?
I'm still looking for a good Android reader app. (And I got no answer to this basic inquiry on this board which I find strange.)