Neat! I purchased and spent a few minutes playing with it and I'm impressed with the general attention to detail. Seems like a solid app.

Tangential criticism: the icon is visually unsatisfying. As in, it is graphically and logically correct, but visually it is like a song with the final note missing. Did you consider using a version with the circle closed? I think I understand the reasoning behind the unclosed circle, but I don't think it is worth the visual dissonance.