I chose a 0. This app is so poorly developed until it deleted my purchases! Why would I buy books to delete them!!! I tapped the oval to reveal my purchases and they disappeared. Every single purchase is gone!!! There's no one to call. No trash to restore them from. Just total loss. I have been a huge fan of Google, though many avid computer specialists have always tried to convince me that Google is the worse search engine, website, has the worse apps, etc. Yet, I would insist on Google.