Are you talking about these?
I havent seen anyone with them. The description says there is a little top end gain (1/2 a second off 60-100 time). I am sure there is minimal gains when driving at low speeds. You probably need to really ram air in there at high speeds to notice a difference. Its more of an appearance mod with small performance gains on the side. If you like the look go for it. I think it looks pretty cool. Has that 1970 look to it. They say its not street legal though.