Actually the underdrive pulleys aren't worthless...they actually make sense if you think about it. I've used them before...its kind of like adding an intake or an exhaust...not an "OH MY GOD!" mod...but you def can feel the difference...the aftermarket pulleys take quite a bit of load off the car...being lighter and stuff....plus they look cool! (well they would if you could see them....You can't see crap under the hood of a BMW)