It's a fair attempt at a unique interface, but I can't help but think it would be better off using Apple's highly-polished interface elements. For that matter, the interface could be just as effective with 3 popup buttons and a text field. This would also significantly reduce the size (10.1 MB really is MUCH too large for this sort of app).

Other issues: No documentation whatsoever. The buttons don't do anything if the tone generator is currently running. The sound is very uneven between tone types and is furthermore generally too loud; even with the system volume at it's absolute minimum it is almost deafening on my headphones. I'd personally like to see the ability to play multiple tones, for work on beat patterns and harmonic series, but perhaps the kinks should be worked out of the current feature set first. It does work, though...