I've had mine for about 7 months now. I am very happy with it. You definitely notice a power boost when your rpms are running up.
I had my chip programming modified with the GM cat back. After this, I added the Cat and the street race exhaust with two dampeners. The car runs great and not too loud. I could probably get more performance with another modification to the programming however.
2008 Redline Sky
White Exterior/Black/Red Interior
GMR Tune, GM CAI Intake, Solo Performance Cat and Street Race Exhaust, Dejon IC Pipes, Sport suspension upgrade, Monsoon Stereo, Opel Short Antenna