I have an FMF Q for my RM, which did the same smoking when new. I think, maybe, it's oil from either the mfg. process, or added just to keep the pipe from rusting or whatever while it sits in wharehouses for who knows how long. Mine smoked like mad for about 1/2 hour of riding (trails not track that day), then tapered off. Did get some comments from my friends.
I also like the sound reduction the Q gave me. I can't campare it to stock as the bike had Bill's pipe and silencer on it when I bought it. But it is much quiter than Bill's shorty (no surprise there I guess).