Great points, and thanks so much for the kind words about the tuner.

Agree that sheet music would be great, and also that the lessons do feel a little quiet / less lively than they could. Your voiceover idea is really cool. We've also thought about adding backing tracks as another way to increase the energy level.

We've also run into that wraparound issue you describe, where a section that starts and ends with the same note can cause an issue when you get to the end and sustain the note. I think you're right about the solution, i.e. better attack detection by looking at the amplitude of the signal.