It won't hurt anything unless you do a crappy porting job. As far as helping, with the T-25 it won't make too much difference - if you have a good free-flowing exhaust (and just an O2 housing won't make a difference with the stock cat, pipe, and muffler still on there) it will help more.
I have a full 3" exhaust (turbo back - including a HUGE O2 housing) and a ported manifold on my car - still with a T-25 - and it didn't make a lot of difference. If I load it up early - like punching it w/out downshifting in 3rd from idle - I can get full boost (16PSi) by 2K, but it doesn't make much difference, downshifting to 2nd is still faster. Also, I noticed that my pressure doesn't start falling off so early. I can hold 16PSi to almost 7K now, where it used to fall off to 14PSi around 6K and 12PSi by 7K.
The O2 I have, BTW, I got from Alamo Motorsports - got crappy service, waited for months (basically it shipped when I offered to come down and collect it), and it came with a downpipe that had to be banged beaten and bent to fit. but for all that, the O2 housing itself was a masterful piece of work. The ID of the collector merge (where the WG and turbine exhaust flows come together) is beautiful - the merge is very smooth and almost linear, and the ID is right at 3". The only complaint I had with the housing itself was that it was shipped with casting flash all over it - first time I took it out of the box it cut my hand. Little time with a wire wheel fixed that though. I wrote a complete review on the Talon Digest after I got it and got it installed. After which Alamo promptly contacted me demanding I change the review to make them look better because they were getting a new manager. Typical.
If anyone was still selling these things, I'd say get it. If anyone has the castings for these, MAKE MORE!!! After looking at a friend's EVO housing, I'm fairly sure this thing is going to provide better evacuation when the big turbo goes on.
