This is what I gathered from the Porsche board. The OBX headers are most likely s knockoff of a name brand header. Quality is quite good, but the gauge of the material is thinner than other headers. One thing of note for Porsche turbos were the welds. Inside the headers, there was a bunch of slag that could wreak havoc on turbos so some guys ended up grinding them down, while others returned them. For a NA vehicle the slag shouldn't cause any harm.
FWIW, B&B headers on my 930 are $2500 v.s. the OBX for $400. I was going to replace the B&Bs because of some cracking at the welds, but opted to have B&B repair them under warranty.