Dynoport will definately be my next pipe, but I have not tried one yet... but they do hae a phone # and they have always been nice and helpfull over the phone... But mainly the metal is thicker, and a more quality fit over fmf... from what I've heard.
I've used both FMF pipes and the DynoPort. The DynoPort is flat-out awesome for midrange pull and is my favorite of these three. It makes gearing changes less necessary for me. Fit is excellent, however, it does stick out to the lower side more than any I've seen. You might want a pipe guard.
Actually, I've tried both FMF pipes AND the Dyno Port on my 96 KDX. I really like the strong mid-range pull from the DP. It allows me to lift the front end over whoops, etc instead of plow through. The pull is enough better, that I don't abuse the clutch near as much. I've bought lots of bolt on goodies, but none of them made me smile like the DP.