The Nasty Jack pipe is their own version of the real MZ65 (not the long thin spaghetti header thing called the clone pipe). Reportedly it has a bigger expansion chamber than most clones. The WC80 pipe is also very similar to it. and obviously the Real MZ65 is always a winner. The Nasty Jack, WC80, and the rest of the MZ clones all still suffer from the same too-big stinger size. That is where the real MZ65 has the upper hand.
None of these pipes are bad though, and on a typical 66cc build it can really help them to stretch their legs since they really come in strong at about 6000rpm and really extend the power up top, often granting a few extra MPH.
What might surprise a lot of folks is how effective the long skinny header clones actually are. In recorded acceleration times from 5 - 25mph those long thin header clones actually perform way better than an MZ65 style pipe. Often reaching 25mph in half the time. Beyond that is where they fall on their face and why most people claim they hurt performance.