Installing them yourself makes them worth it. I got mine free from helping return a friends car to stock so he could move into an 04 Cobra. Im still on the fence as to how much power has been added. It pulls much harder up high and with my 4.10s I get there quicker. In the future a dyno tune will help even more and hopefully I can get some down low. The sound on the other hand, talk about turning heads. I have the full Mac system BTW.