Good Learning Tool
No, it was not clear to me that you need to buy songs individually if you want more than the 3 free songs. However, there about about 45 different songs, and the app seems well made in my opinion.
You can not load your own songs, although I don’t know how, why, or what would make you think you could after using the app. It seems like the creators recorded each individual part of each song, and made an app to cleanly and easily separate the different parts. Perhaps you could email them and request a song, but this is not an AI generated “do-it-yourself” kind of app. This app is a well curated teaching tool.
If you have wanted to learn harmonizing for a while like me, I’d say this is a good start and worth the money.