I heard that to, but i had a HKS mushroom pod on my car for over 100K kms (also ran distilled water as coolant, left more than 7500K kms between oil changes (castrol R FTW) and even had a MBC (ohh no's!) for well over 50K kms) and my mech. inspection at Bluestar (after the 180K kms proper service) came up great

Maybe i just got lucky with a decent engine and/or avoided rocks