because the stillen are popular as well as the JWT and also help prevent with loss of power from heatsoak. The fujita and jwt will cause you to some power loss due to heatsoak without proper heatshield.
So far from my knowledge and the G35driver.com, that JWT are more popular for the 350z owner due to the hole intake at the front of the beam, while the V35 not as good. G35 in USA seems alot more popular using the stillen, being the one that having a good heatshield and prevention of heatloss. Also help with the problem of getting defect by cops too.
This is purely owners choice, if you just want sound then JWT pop charger. if you want sound and less chance of power loss, then go for stillen.
I just want the OEM looks and don't want trouble from coppers as well or even upgrade to the 06+ rev up intake box.
cheers