My BPV sound has changed alot. I have the turbosmart dual port. It has a choked sound most likely due to the 90 degree elbow. I also get fluttering when letting off the throttle sometimes. I'm sure it can be taken care of with some careful adjustments, I just haven't felt like taking the time to do it.
I believe the core is a little smaller than the COBB core... either way you're going to have a much different sound regardless of the type of bpv bov you use, my HKS bov went from minor flutter to becoming a lot more sustained and a lot louder.. but I like it.