I love finding new apps for my piano students. This one is very user friendly and drills on some basics that add nice variety for my students.
The only part I found confusing was the couple of places where you must drag the answer box instead of just clicking it. This was not clear and no instructions were provided. I figured it out but it would have been nice to have this in the instructions. And to access each concept you just tap on the list in the settings menu. After you see these two things, using the app is very easy and it is fun to use. Great job! thanks.