That's what I thoughtDevious2xs said:I see no reason or need to "regulate or homogenize" the exhaust gasses. The oxygen sensor only works at low throttle positions. There is plenty of gas mixing happening in the header without the "homogenizer". Also, why would Zard feel a need to do this when others do not?
It is a flow restrictor that may help reduce noise by acting like a baffle.
It is likely in place due to some noise or power limiting regulation in the EU. Zard seems to have several versions of their header and silencers depending on where they are sold.