I like KOReader, but gave it up in favor of the default software on my Kobo Clara BW, mainly because of library navigation. I prefer to keep all my books on the device, but the only way to find them (as far as I can tell) is by author. I haven't had the time to go through my whole library to fix the author sort, and it became a real problem to find books I already possess that I want to read.
Fortunately I didn't delete KOReader, so all my setup is still there if I find a reason to go back.