Although i cant speak for REVO, i have an S3 and have had it remapped by both bluefin and GIAC, the difference in power delivery seems huge GIAC being the better of the two, i remember taking the bluefin map off and not feeling much difference when the car was back at stock, which prompted me to try out GIAC, i have no regrets about spending the extra money.
The general consensus seems to be that REVO delivers lots of power early on and tails off later, GIAC on the other hand is smoother but pulls right to the red line, the increase in torque really pins you into your seat.
Had mine done by statller in sheffield and cannot recommend them enough, top quality service.