Both get a big
from me.
The Billetflow/Reichard Racing Non-slip 2.76" blower pulley netted me as much as 120 ft lbs and 80 hp through certain parts of the power band.
Peak boost is now around 15 psi during the day when it's around 60 - 70 degrees, but it's hit 16 at around 30 degrees.
The single 100 mm idler pretty much eliminates any belt slip. LOTS of belt wrap on the supercharger pulley.
I have seen no signs whatsoever of slippage. Also, I'm not seeing any dust at all so it doesn't appear to be too hard on belts.
Doug at Billetflow was very helpful and a nice guy to deal with. Talked me out of spending the extra cash on the 4 piece idler set - the single gets the job done and the 4 piece is mainly for looks.