Thanks for the information about adding protection. I wasn't sure how much use it would be, but if it actually works I guess it's good to add it. I'll definitely look into those links.

I'll definitely experiment some with the pricing as well.

The account permissions are needed since it uses a SyncAdapter to sync the progress data between multiple devices, so if you have both a phone and a tablet you can sync your progress between them. The sync functionality is also used to fetch updates to the word list when I correct some translations etc on the server side. Unfortunately, there's no way to use the Android sync functionality without also setting up an account (as far as I could see), and I didn't want to implement all that by myself.