I don't have it mine (yet) but I've driven one and was very impressed, although the car also had a downpipe. The power delivery is incredibly smooth. I've had GIAC software in a MKV GTI and a MKIV R32 and was very happy with both.
I'm leaning towards GIAC also. There's a place not too far from me that will be able to bench flash it in the next few weeks. I've heard some very good things of GIAC from people that have had their tunes. When are you getting yours?
Also - have you seen this cool vid? They are coming out with a bluetooth app!
I have it and at first I was okay with it now, however, very impressed. You have to drive the car like you stole it, i.e. meaning over 3,000 rpm. If you drive your car in auto Stronic don't waste your money, however, if you drive your car like a true enthusiast, a manual or Stronic full manual you will really appreciate this tune. For passing this thing is a machine. Keep her above 3,000 rpm and you will love it.
Here is a link to a dyno video of a local B8 S4. This car was using our Stage 1 software with an AWE intake and catback exhaust. Our bluetooth switching module is now available, and we are in the development process of an iPhone switching device. Feel free to email or PM me if I can answer any questions!