Every time (maybe every other) you play a tone, you'll get a popup ad, sometimes with sound and video. Prepare to be annoyed.
I get that app developers deserve some way to monetize free apps, and I agree wholeheartedly, but here's the thing. I've developed apps (had 4 in the store a few years ago), so I know first hand how easy it is to use the CoreAudio system to play a sound. The only innovation here is the slider to control the pitch. The constant advertising, therefore, is just a cash grab. I'd have been happy to pay a buck to turn off the annoyances, but there's no option to do so.
The app does prompt you to leave a 5-star review to turn off ads. That's obviously been successful in getting the very high rating. Nice trick. Nagware, it's called.
Uninstalling as soon as I push send on this review.