Success is a factor of expectation.
My 03 handled terribly, anything would have been an improvement. I think factory design was not wanted either. For me, it was not just about look of lowering, more about how it handled, esp. hitting hard corners & sharp lane changes at speed without fightiing with a bunch of roll.
My brother had a GXP, totally differnet ride. I wanted to upgrade to get a ride closer to what stock GXP has. Depends on what your looking for? Lowering? Handling? Adjustable?
C/o definately comes with sticker shock. But I did the math. The kit, w/o struts, was $350 for fronts. The springs are $100 pair. That means the kit, w/o struts or springs is $250, thats $125/corner for; threaded sleeve, adjuster nut with washer, custom top plate, hardware--you just need to buy silicone sealent. Now add up tradition build, top plate+bumber+boot+isolators= not that much of a premium for c/o. BONUS--b/c there is no spring perch & you can easily, quickly lower spring so it is not comprssed, c/o are 10x easier to get on and take off.
The thing that made the most sense moneywise for me was to buy a complete strut assembly, but there is not un 'upgrade' option for that. A c/o kit lets you select strut, spring compression rate, and ride height, all independant of each other.
Over-rated? I don't know. So far, I got what I wanted.