I had HKS SS BOVs. Can't comment on other brands. But I think they look good and sound the loudest! :) The main purpose of having them is let people know I've got a modded turbo car and don't mess me! :) I loved passing people/cars at full throttle and let off when I was next to them. It supposedly prevents all the air going back to the compressor when throttle bodies are closed. The quicker spool up between shift theory is after all, a theory. I've not noticed any difference on stock turbos nor bigger turbos.