It was fun for a while but it's obvious that the developer has become quite greedy. The asking price for Plus is far too much for what amounts to a simple series of sentence exercises. The later exercises are typing-heavy which is incredibly irritating on a phone. Once I learned the basics of my target language, the app became redundant and expensive. The free version is fine if you don't mind being bombarded by ads and up-sells. Don't bother competing on the leaderboards with the free version.