I have been studying Chinese for 16 years, and teaching it for more than five years. This is hands-down not only the best Chinese writing app that exists for iPhone, its the best tool for learning to write Chinese characters in general. The fact that you can create your own packs to study from makes it invaluable. Theres plenty you can do with the free version, but the expansion packs are also reasonably priced. I hope this never goes away.