They are noisy, run with more friction than glass reinforced plastics and the guide pulley has a fixed bearing, which requires absolutely perfect gear adjustment. The top pulley in a Dura Ace wheel is a great piece of engineering.
I can only speak from my experiences as an owner.
They spin far more freely than an XTR jockey (I don't have a DA one to compare to) without any doubt, by some fair margin
Precise derailleur adjustment is no problem. I'm Cytech 1, so nothing special really, just an average bicycle spanner monkey and have no problems with a tight, slick, precise adjustment of the mechs only anyof my bikes.
I haven't noticed any extra noise, bit will listen in tomorrow when I ride it cross country to Milton Keynes, although as I haven't noticed in almost a decade I'm guessing any extra noise can't be significant.
Like the OP, I had a damaged jockey wheel and balked at the price SRAM wanted for X9 jobs, hence the KCNC ones. In a decade of ownership my only complaint is that the anodised finish attracts the eye, and they look grubby very quickly