Every tiny mistake will invalidate a whole written answer. After you advance more on the course it gets very hard to complete a lesson without having a premium account (infinite hearts). At this point, it is not motivating having to take the same lesson over and over again. It is infuriating. I don't believe this app deserves my money. I have used this app for a long time and this is a well-formed opinion. If you're not willing to spend money, don't download.