This sounds like it could be a really interesting tool....although at £50 for an individual track I'd want to see the feedback criteria which the music would be reported on....if it was just a box that says 'tell us what you think about this song' I imagine a lot of people will just leave the box empty or put something unconstructive.
I'll definitely use it to listen to new music and give others feedback though!
But I think this could definitely become very useful for songwriters, especially if gains more listeners
EDIT: also just noticed, you mentioned that this was a free service, but on the site it says it's actually £300/10tracks £100/3tracks or £50/1track. I think if the prices were more reasonable or even free then this could be massive for songwriters etc.