I love Yousician, because it is a lot of fun to play.
However, one comment I have is that it does not teach you a specific classic piece (piano or guitar) that you can later on play (also without the app).
It would be great to have a training path to some of the classics (for example Moonlight Sonata, Bach prelude in C, etc.), with specific exercises for some of the more difficult parts.
As a result after completing an exercises you could actually perform the piece without the help of tablet/phone to show you friends and family.