Monthly subscription

You'd have to offer a monthly subscription, because paying a large sum all at once is a deterrent most of the time.

You don't know if you really want the app all year round, which is my case.

I really enjoyed the free trial, but I don't know if I'll stick with the app for a whole year, hence my suggestion of a monthly subscription. After my free trial, I wanted to subscribe, but no monthly payment was offered... too bad...