one of my friends "Keyshawn" was one of the first celicas to be boosted by the XS kit. He had a few small hiccups but put 100+k on the stock motor and it held just fine he says. Though I have read horror problems with casting problems of their intake manifold etc.
There was an issue with the pre-production filters as well. I have one of their kits. The manifold has been marginal but overall I think it was a really great kit. I'm actually going to be selling it with a new manifold for really cheap shortly.
I have one of the prototype kits as well. It had the same air filter setup yours did. I just called XS and bought the production filter. Really, the original setup wasn't bad if they had taken two seconds to apply some plastic glue on the threads of the inside of the fitting so that they would melt together and never come off. But hey, that would be too smart, right?
The "tune" they provided in the PFC was also utter crap. But that's pretty much standard (if you get a map at all) so it isn't something XS sucked at worse than anyone else.