As stated, the Nissan snorkel is manufactured by Airtec. If you get Nissan to install it, be prepared to open it all back up and seal it yourself, because for some reason - and I'm gonna ask my dealer about it, seeing him again on Wednesday - Nissan dealers won't seal the thing up.
That's the difference between Airtec/Nissan and Safari. It's not that the Safari is better at sealing, it's that most people who get Airtec/Nissan get 'em supplied by the dealers who don't want to seal them properly, and Safari is supplied by aftermarket guys who DO seal them properly. It stands to reason that you'd observe that Safaris seal better, but knowing WHY is also important.
If you like the snug fit of the Airtec (compared to the very prominent knuckle of the Safari) then go to TJM and have them sell and fit it for you.
As it happens, I have a nearly full tube of Sikaflex in white. I've used maybe 30cc out of the whole thing and I'm eyeing off my snorkel ... I just don't know how to get the airbox out so I can seal it up properly. It's something I will probably do tomorrow arvo if I get a chance, and I'll take pictures so everyone can see how dirty my engine bay is *cough* so everyone can see how an amateur does it.