BBF and frankf, you are both certainly right. There are other ways to toe in a speaker, and some of them will be more accurate. This is a very quick and easy way, especially if you are alone. Ultimately, your ears will decide.
BBf, you are correct, it doesn't take any audio measurements.
Still, it is nice to see some innovation, and $0.99 isn't much of an asking price, so I am in favor of it. If the app was $5, $10, or more, it would be a different story.