Depending on your goal, the "solid features" differ significantly:
Seamless synchronization across devices. You can start a book on your Android phone and pick up where you left off on a tablet or web browser. Library Book App Android
These apps connect to your local library card so you can borrow ebooks and audiobooks for free. Depending on your goal, the "solid features" differ
Widely considered the gold standard for ease of use. Depending on your goal