Easy to use
The first major positive I noticed was that the installation does NOT ask for intrusive permissions like so many so-called free apps (it is never clear to me exactly why these need access to our contacts etc..). I tried the first level of characters, the app gives some encouraging feedback when the answer is wrong but close, true to the educational intent. Otherwise the first screen is a little slow to load on my Samsung 10 inch tablet.
A good start and I like the focused vocabulary idea, although I'm not interested in the characters, only the pinyin.