Installed my CTS DP this evening. It took about 2.5-3 hours including setting up and cleaning up. All in all, it was a fairly easy job, it was just kind of a pain snaking the stock DP out.
Overall I'm satisfied, sounds good, looks good in the engine bay, and it feels like there is more power. The one thing I am unimpressed with is the crappy clamps they include. The hardware was so jacked up I had to chase the threads on the nuts and bolts to be able to get them to go together!
I guess that's what you get at that price point.