Not on these...but you need more than just a handheld to reap the full benefits from something say: HPT. I noticed a huge difference with my car after we tuned it.
I have the 3" catted ZZP downpipe, I'm a fan. Which is huge considering it's ZZP and I never care for them. I also got the Intense Upper Poly's (square and circle insert).
My GXP had a pretty ugly looking downpipe, still looked like a partial U-Bend anyways, and unless you tune the code out for no cat, the remote start won't work. I noticed decent gains just from that, the open cone, and poly mounts. Tune really pulled it all together.