I suspect that this lags and does not react upon pressing the button. When you're doing clicker/sound training, the dog responds to the cue -- if the app lags, you're reinforcing whatever happened after pushing the button on the app. The waveform may be visible, but you can't be watching waveforms when training a dog. It's also very easy to miss pressing the cue if you can't stare at the screen, so you may not be producing the app's dog sounds. It would help to have an option to turn on human audible sounds, but unfortunately, it doesn't solve all shortcomings. Maybe it would help if there was support for a physical Bluetooth clicker, but even then, there would have to be no lag.
By the way, there are ads in this app after the initial $2.99 download. That's just inexcusable and greedy, not to mention that it's really distracting when you hit an ad instead of the clicker button -- people pay for this app and have a right to know that it has intrusive ad banners.
You're better off spending $2.99 on a physical clicker or whistle and know that it's accurate. I got this for free today on a sale, luckily.