I've used it a few times. No problems to report. I did run into an unusual situation with one book. I wanted to transfer some money into Firepay to use somewhere else and was told they couldn't send money to my Firepay account if I had not sent money into them at some time using Firepay. I hadn't so I just blew it off and handled it a different way.
Recently I have had two books in CR (after someone on here told me they could do it) transfer funds between my accounts with each of them. ( Sportbet.com and Optionsports.com ) They did it with bank wire transfers in about two hours and didn't even charge me the bank wire charge fees. I am glad I found out about that because that is the cheapest and easiest way yet I have found to move money between books.