I have not tried Libby yet but recently started checking out eBooks from my local public library (via Overdrive) to read on my Kindle. I am pleasantly surprised how convenient and straightforward that process is. And all that without spending any money.
Libby is the new and somewhat flashier version of Overdrive. My old Android tablet doesn't handle it as well as the old overdrive app, but it works. I think it also has better support for multiple library cards than overdrive, but I haven't tried that yet.
