I really liked this App, especially the drawing system: I really appreciate seeing the curves drawn by myself during the reviews.
I have been using KanjiTree App for a while. It also has a very nice drawing system and custom kanji set creation capabilities (pro version). But unfortunately it has no SRS, which is truly missing.
I decided to upgrade, I have not done it yet but I will do it very soon 
I personally really enjoy writing kanji on my phone with a touch pen while commuting to work 