My rating is for the mobile app and does not apply to the desktop/website version. In short, the hearts system completely ruins the learning experience. The frustration is made exponentially worse on difficult lessons (where you make more mistakes by necessity) because you will be hindered from making progress by Duolingo's attempt to push you to premium. I understand the need to make money but at worst they should offer the choice to watch an ad to complete an ongoing lesson, not force you off.