Sorry for the late reply
I want to clear a thing that I support this as long as the engine bays are difficult for the traditional setups but as for the 350z....I really find it absurd as there are other traditional kits which are cost and performance effective rather than rear mounted one's
About lag ....You don't really notice it on big V8's, plenty of engine displacement to move a lot of air though the long pipes. Also The turbos are set up quite a bit differently from a traditional setup and it all but eliminates lag. Spool-up time is quick and they (STS) try to compensate for the distance by reducing the diameter of the piping, thus increasing the response time
Isn't the bypass valve just a flapper that remains closed unless the filter starts to suck up something heavier than air?l