I'd like to add that the harmonics remain undampened regardless of a smooth install and regardless of whether the pulley is OEM diameter or underdrives...
If you want an aftermarket pulley with a damper...
FluidamprŪ Harmonic Dampers Made in U.S.A.
Nothing against NST -- they make great stuff, and I have bought supercharger pulleys from them before that fit perfectly and worked great. They make excellent products.
This is simply an engineering issue... undampened harmonics put more stress on the crank -- period. Whether or not that matters (or at least the extent to which matters) for our application is, I think, unclear.
I think GTM Sam's commentary was spot on in the 600 whp SC thread, and everyone considering an aftermarket crank pulley should read it and think on that before buying.
But again, I try to err on the side of caution...