They look the same because the can only bend one way. The after market head pipes are different lengths most are a little longer. I have the Yoshi and it moves the bend forward a little. It is great because now the header is further away from my leg. I don't burn my leg hairs off if i'm cruisin with my etnies and shorts. i never ran just a slip on but I have very experienced friends who race and they swear by using a headpipe. :evilgrin
mich pretty much hit it on the head. aftermarket headers usually have much larger headers, increasing power. so, youre spending 200-300 on a silencer, why now drop a few more and get it complete, the way it was intended? ya feel me? :blah
It depends on your application. Even HMF does not recommend their full system on a 400EX for certain applications. If you look closely at the dyno numbers you see why. Some applications need the header, some start with a header that works as well or better.