Now that I've tried FBReaderj I thought I would add my impressions of that app.
Sadly, my first impression was not promising. I downloaded and installed the App and then copied one of my Fictionwise Multi-format ePubs (Waterfront Fists by Robert E. Howard) from Aldiko's ebooks directory to the FBReaderj Books directory.
FBReaderj could not and still can't even see the book in its Library.
Next I went to Feedbooks and downloaded a Murray Leinster book (Operation Outer Space) and that loaded perfectly. Reading was similar to the other two apps, and as promised, books did seem to load more quickly (especially in comparison to Aldiko - which feels fast when reading but not so much when loading). One thing I did like was the Feedbooks integration.
The book I downloaded had links to Leinster's other books on Feedbooks, and clicking on the link automatically downloaded and opened them.
That, I thought was cool.
Overall I thought it was a decent app, but getting books in was a bit more work than I wanted.