Had Pypes LT's on my '08 for almost 10 years under my ownership (still on the car as far as I know). Never leaked, no material breakdown, just typical discoloration common for cheap headers. Could always clean them up fairly well with a green scrub pad and alcohol. Nothing can take off the heat discoloration, but definitely can keep the shine on with engine detail intervals. Performance-wise, expect similar results as you would from a legit set of kooks.
For the record, would absolutely buy again.
For the record, would absolutely buy again.