I have no first hand experience with them, but from what I have read here in many posts is that an exhaust will not provide any sort of of performance gain. The only benefit of an exhaust is if you what to change the sound of the machine.
I have the FMF and while I didn't do the before and after performance checks here is what can tell you,
It is at least 5 lbs lighter... That is at least a small gain
It does sound seem to rev quicker off the line
The sound is just better... Everyone that has heard mine next to a stock exhaust raves over how it sounds and while it is louder it is not so loud that it draws unwanted attention from the LEO.. I went riding up Bee Canyon near Hemet and at the staging area the Ranger came by and checked us out.... No problem...
And it looks really nice.. I did the single exhaust they do have a dual exhaust too.
And it is priced well as compared to a lot of the others and it fits very nice....
The one I have is directly from FMF off their website... When I made my purchase that had a 20% discount going so there was a good savings from what Polaris was getting. It has the FMF logo. You can see how they look on their site.