No experience with the RP, but my ST-E2 has worked fine outdoors as long as there's LOS. Indoors, it works really well bouncing off walls. I also have used the Cactus on studio strobes. They are cheaply made, are prone to interference, and isn't very reliable. Can't argue with the price--I just get extras. I also have the PW II's which are the best in terms of range and reliability, but they cost too much.
One day, I'll have to invest in the RP Px series for E-TTL.