Completely satisfied by it, but maybe a character-drawing feature could be built into the phone version? Are there apps that do this already?
I don't expect DL to introduce specially-designed writing exercises, as it has never taught handwriting for any other language. However, most mobile devices have half-decent Chinese handwriting inputs anyway, nowadays, so merely having the option to select manual input on the app (as it is on the web) would allow users to practise writing if they so wished.
I seem to recall that HelloChinese and ChineseSkill do have writing exercises. Quite honestly, however, writing things out on paper is far more effective; no-one writes with one finger, so one will never develop the same muscle memory from writing on a screen.