I second that this system is first class. The flash units are not much different from the 580EX but the addition of the RT has made all the difference. I must say that they are even that much better when combined with the ST-E3-RT. I have been able to put away all my other methods of flash triggers.
My problem is that I want 4 more of these.
Note that they only function to their max (speaking of group function) with the 5DIII and above.
I posted this limitation last year and will be glad to review it if anyone is interested.