Me and my fiends went a very similar path with a different product. We made an Android and iOS app that would help learn programming by wring actual code. Users loved it. They were spending 10 minutes in the app on average! Some spent over 2 hours a day and would finish all the content in two days. Even though, nobody wanted to pay for it. We figured, we would never be able to bootstrap with ads alone so we had to focus on something else.