I use codementor as well, as a mentor primarily. Got a lot of clients through them, including longer-term clients for my consultancy.

Immediate feedback: If you want me to sign up, 75¢/min is too low, and you do need a mechanism to raise rates. My standard codementor rate is $2.25/min (and goes up to $3/min on some specialized skills).

Feel free to email me if you want some feedback/video chat. I was on hackhands back when it still existed. I'm a sucker for these types of platform. I especially love getting clients looking for actual coaching/mentoring, not just debugging.