can these really add 10% power??!?

Was looking at these:
http://tuningevolution.com/eshop/catalo ... cts_id=271
They look nice but surely the 10% power increase in bull is it? They seem very cheap for a stainless header??
http://tuningevolution.com/eshop/catalo ... cts_id=271
They look nice but surely the 10% power increase in bull is it? They seem very cheap for a stainless header??