I had an sps which I kept (and used) on mk4 golf turbo, 8lS3 and mk1 TT all revo mapped.. Loved being able to switch back to standard, mainly so the garage didn't get to thrash it about lol.. Only thing I found with the sps was that it has to be done with the ignition off.. I think it was something like: ignition off, turn switch on sps to desired setting, plug into obd port, wait til sps starts beeping, switch ignition on!
So I started leaving my car on stage 1 so I wasn't tempted too much and didn't get bored of the power... But then you run into a problem - one day an m3 comes next to you, and you want to be on stage 3! so (at 70mph) you put the car in neutral, turn off the ignition, plug sps in, turn back on, voila...! Lol just don't turn the steering while the ignition is off.. This is the only (unsafe)way i found to change the map whilst in motion
oh yeah, just to add.. This was easy on the mk4 golf (obd just in front of gearstick) not too bad on s3 8L (by your right knee) but I can see it being a pita, if not impossible on the 8p3.. The obd port is tucked right away!