I know the local fast drag guys use them and swear by them. My understanding though is they are meant to be used with the dust seals removed, which is part of their better rolling resistance.
I have already removed the dust seals from my 00 and it makes quite a difference in rolling resistance, though it makes mounting the wheels on the bike a pain in the butt as the have the physically hold the spacers as you install the wheel.
I hope to get ceramic bearings (one wheel at a time, I am poor

and then have some custom spacers made that wil stay in place.
I also hope to ride fast motorcycles everyday and have sex with super hot young chicks everyday , and that rarely happens
But hey, percentage wise, some of it eventually has to pan out...lol