Exhaust housings are cheap, readily available from Garrett and others who are changing theirs and one of the easiest things to swap out there. Not having to re-buy a turbocharger down the track because you've decided you want more power can outweigh the less than ideal lag in any case and as he's said already, he doesn't care. I've driven 4 x std RB25 R33 GTST's with GT35's ranging in rear cover size from .63 to 1.06 (my own) and have come to the conclusion that they're a fantastic turbo for these motors for both street and race use. They're loads of fun and offer a bunch more potential than a high flow or similarly sized unit.
Spitting out a bunch of brand name parts just for the hell of it and claiming that they're required is just nonsense as proved by many many users on here and elsewhere. When giving advice, try to deal in fact.