[Sefiriot]

Tried most of the free reader apps out there before settling happily with Moon+ Pro. I use CC with M+ Reader, and it's going pretty well so far. I'd suggest looking elsewhere for a PDF reader app though; I like(d) Duokan reader for PDFs, but the adverts are irritating. Still hoping there'll be a reader app out there one day that doesn't drive me batty trying to read PDF files.

If you just want a listing of all the books you have available on your reading device and aren't too fussed about organisation, importing them into Moon+'s database is probably enough. However if you're looking for a more nuanced and easier way to sort through your ondevice library, Calibre Companion's definitely the way to go. It's become an indispensable app for me, since it works almost like a mini calibre on my phone (minus the ability to edit metadata and covers that is)-- sorting and searching by tags, authors, date added, etc. makes it easy when I want to browse. The Content Server interface in CC is also very nice.

Best of all, I can personally testify that CC can handle an on-device library of 10k; possibly more. My current count is 12650 files; however I've had some issues that seem to be from device/system issues and my overly large library. Otherwise it does what it's supposed to with barely any fuss. The metadata sync time as your ondevice collection grows is the huge trade off there however, but even that's gotten pretty fast.