Looking pretty good! I haven't tested extensively yet, but two things I just noticed: 1) The target "buttons" for assembling the hand don't look like buttons at all. I thought it was some stylish filler wallpaper until I accidentally tapped it. You may want to draw some hard lines or something in there so it's clear that you can touch it, and that it's not just art. 2) The toggle switches for settings like open tanyao sometimes instantly revert. I got it to work by touching and holding briefly instead of quickly tapping on them.
Mahjong Helper & Calculator at Google Play market analyse