They all do the same thing - the sound & look is the only thing that distinguishes different brands. As far as function goes, its basically pull type vs push type.
hell, out of the 2 turbo builds ive helped with both have used the ebay greddy knock off without any problems. Turbos are still in perfect working order and the valve responds as well as you could want...dont know what else to say.
If you got the dough - Tial is the best you can buy. Otherwise, 1st gen DSM, or Ebay knockoff Greddy BOV. I think Blitz and HKS BOV's are overpriced and played out. Where you want to spend your money is on the wastegate - thats what keeps your engine from overboosting, and going boom.
