beautiful interface, great tool
I purchased this app a week ago and have used it for every violin lesson I have taught since. The students are able to place their pitch in the context of the overtones, providing a much better tuning tool than a simple tone given on a metronome. The interface is easy and enjoyable ... my students love playing with it. I have not gotten deeply into the nuances of the various drones ... I've found a few favorites (the evolvers and some simple sine waves) and stayed with them. The included info seems comprehensive and excellent. The application is vastly better than DroneStation, the other tool that seemed like a possible contender.
Only minor piece of feedback is that I spent 30 minutes looking for how to turn the drone ON and was ready to give up and email for technical support ... discovering finally that the only way is to use the overall volume slider. It would be nice and also more intuitive to have a simple on-off button in addition to the volume slider.
Overall, great application for my purposes, and well worth it compared to over $100 for a traditional Indian drone box!!