I was the first GIAC flashed mk6 in Oregon. I have been really happy with the performance throughout the 15k miles it has been used.
You cant clear codes with the GIAC handheld unit, just change the different programs you bought with the pump flash. If you bought ONLY a flash, you would NOT be able to switch back to stock. GIAC charges extra for that, along with the fee for the hand held device and then if you want valet, 100+ octane files or whatever else. Unless you buy during a sale, I think that APR is less $$$.
I am happy to answer any questions about the flash or anything else GIAC related. You can find all the tunes they have available for the mk6 at:
http://www.giacusa.com/programs.php?mpid=619
FYI - They show a flash for the 2011 GTI, but its the euro version with the lower level security ECU.