i posted this same forum about 3 months ago. it really depends on which one you get. there's the pencil type kind that companies like streamline, denton, jpmx make...then there are the more expensive ones that are like mounted on your bars that companies like elka, gpr, precision make. I have a pencil kind, the Streamline billetanium, got it for about 150 bucks on ebay...I noticed a difference right away, I can definitely go faster in the field sections of the races. But, you have to remember that it's stabilizing the bars from being jerked out of your hands, so you will have to adjust it to fit your riding style. The first race I did with it, I had bad arm pump not even two miles into the track, I adjusted it to not be so hard, so it was easier for me to turn....
I really like it, I think it was worth the money...I know the stabilizers like gpr and precision are better than the pencil type, but I cant say much about them, I've never rode with one on.....I hope this helps, if you have anymore questions, just ask, I'll try to answer :)
ps...how wierd is it that I'm givin you info about something related to quads? ur the one that usually has answers for everything!!!