I can't say I've used it but I can definitely say that I never will either.
I can't trust registerfly with a 60c domain let alone a $$$$ sale. If I was to make a large sale I would rather place the escrow in the hands of a reliable company than a pack of jokers like registerfly. It'll probably take forever and the buyer will pull out. I'd rather fork out a bit extra cash to know I can sleep easy at night. But that's just my opinion and if you have used them and it has worked well then good on you and hope it continues to.