I loved this app when I first got it. But now The sound does not work on my iPhone 6, and it appears the app and the website are no longer being updated. But the wheel still turns, so its still useful for transposition and, to a lesser extent composing. You just cant use it to listen to chord combinations. Its kind of like the app has been reduced to an iBook.
JSLsurf about The Chord Wheel, v1.1