2 stars because this is an amazing learning app. BUT the heart system & the leaderboards make it not worth the time. I enjoy learning a new language but $80 for an app is STEEP (for me). Also, most of us want the option to join the next leaderboard, not be forced into one each week. Not in the top 10, stay or get demoted? Unfair. You have to spend a lot of time on Duo to keep your daily streak & leaderdboard position. Only 2 days MAX for a freeze streak? I have a life outside of this app.