I like this idea, but I feel that the UX needs work. I'm not musically inclined, so take anything I say with a grain of salt, but...

I'd expect to see the note I'm singing on a staff, highlighted on the keyboard, or both. Naming it with the 3 lines is good for targeting in on the note, but it needs more context for beginners.

Also, it seems to lock in on the note? I couldn't figure out how to get it to let me switch to another note without stopping and starting again. Which means it isn't great for practicing a sequence.

Great concept, though.