I think it's a GREAT idea. Now, this might just be me, and I don't want to sound negative, or take anything away from the effort you've obviously put into making this really good, but ... For $120 / year I think, hmm I could probably build something that does this (just for me) in an hour, and it'd be fun! However at $10 per YEAR, I would think it's a steal and jump at it. Not suggesting you should drop your pants on…
Certainly for an agency to do this will cost them more than an hour of developer time. $120 per year is a steal, OP should add different pricing brackets to capture more value from bigger agencies.