I only use the mobile app to keep my streak, the app design is good but for real practice I use my computer. The heart system discourages me from spending more time using the app, and I have been using Duolingo enough to know that it has mistakes and they feed from users to correct those mistakes. Everytime they came out with new lessons on a course they are full of mistakes and I am not paying for that, it is not worth it. There are better options, like a real course