Recently purchased through Dinan but I have decided to go another direction. Pulley Kit for sale is brand new, never used.
From their website:
"Dinan's lightweight crankshaft pulley is constructed of Aircraft grade billet 6061 aluminum that is anodized black and engraved. It does not modify factory harmonics or dampening and safely underdrives the belt driven water pump, alternator, AC and power steering to reduce parasitic power loss on the M3 engine. It produces a peak gain of + 11 horsepower @ 8400 rpm and + 7 lb-ft torque @ 8400 rpm on a stock car. The kit includes lightweight pulley and shorter belts for bolt on installation."
Pulley Kit is for 2008 models with 6mt made before 05/08. BMW changed from a single-sided belt to a double-sided belt for M3's produced after May 2008. Those with a 2009+ M3 that are interested would need to contact Dinan for the double-sided belts. Can't imagine the belts being too expensive.