Several weeks ago, the Music Theory Pro app was updated to Version 2.0, and some features were locked under an in-app purchase. The developer received feedback and changed the app so that all the content is included in the purchase price ($4.99). I love to see developers responding to user feedback.
Music Theory Pro fits into the same category as several other theory apps, such as Tenuto and Theory Lessons (basically musictheory.net). Simply put, if you are a serious music student (high school or college) owning this app (actually, owning all three) would be a great way to reinforce your study of music theory–as well as to add some ear training exercises into your study of music theory.
If you would like to learn more about the Music Theory Pro app, check out their website.