this came up a while back. I called power now about them, and they actually discontinued the 700 power nows because they didnt do a thing. This was straight from them.
Like was already said, on carbed bikes it "can" make a difference. On the keihin's it seems to have a noticable effect, but on throttle bodies/fuel injection they dont do a thing.
Scary fast power now said that the intake on the 700 was already really smooth and placing there piece before the TB did absolutely nothing.
these are completely different then a throttle body spacer. TB spacers make the air spin into a vortecy. The scary now power valve slices the incoming air and speeds up intake velocity. While they are BOTH suppose to do the same thing, they do it totally different.....AND, I have yet to see a TB spacer do anything at all. The power now's on some dirtbikes have proven effective.