I'm going to trust the developer on this one – Auto-Tune Mobile Review

And give it 5 stars, which it easily deserves, even though some are reporting some technical issues. They'll fix it. This app is exactly as advertised. It's absolutely amazing, especially for people like me that have a lot of technical musical knowledge, but simply can't sing perfectly on pitch. The documentation could be a bit better, but it's pretty straightforward. For the people who don't think they are getting any effect, try hitting that huge green BYPASS button in the middle of the screen and see if that helps. So glad to see this app is still supported. It's an incredible tool in the Audiobus/iOS family of must have apps.
Review by Shrikke on Auto-Tune Mobile.