***EDIT***(Was editing my post when you posted and this post ended up below yours) :shrug:
Pretty much no more missed shifts, smooths out the "shift" for easier shifting
Basically what it does is lets the roller on the shift drum lever arm, roll over the rounded off points easier.
AND yes, you can bang the gears easier and not miss shifts like you would sometimes.
I have one for sale in the (for sale section) a guy said he wanted it but has not bucked up, so it will be up for grabs tonight if he don't want it anymore.