I like the concept and using a voice-like sample for harmonies is a good idea, but I found the interface a bit difficult to interact with. I had trouble creating a good-enough main melody, especially when trying to make two notes sound at the same time (my keyboard may not be in its best state right now :-/), and that made it hard for me to properly evaluate the harmonies when everything sounded like a mess to my ears.
It would be nice to include one or a few demo songs to try out the less musically-inclined people like me :-)