I used a Dynomax ultraflow welded when i did the side exit setup on my old Storm. It was the straight through design 3" in single 3" out. It was really loud, but had an awesome rumle to it....especially at idle. Dynomax makes some good sounding mufflers.
I used the 3" inlet/2.5" out welded muffler with the stock B-pipe and aussie 3" DP.
The piping ran exactly like stock, I used a 3" mandrel bent pipe off the stock b-pipe and 2 - 2.5" mandrel 90s.
The power was great, I gained an extra 3psi of boost. It sounded as loud as an apexi exhaust, but crappy.
I used it for a day then packed it up and returned it.
Too loud for my tastes and sounded bad.
I had a dynomax ultraflow on my WRX, 14x4.5x9.75, 3" in/out. It replaced a 14x5x8 3"in/out Magnaflow, and I liked the Dynomax better. About the same volume (not bad - and I'm picky about this stuff) but the Magnaflow was much more bassy and therefore carried more. Also it droned at cruise, whereas the Dynomax did not. Just my opinion, if I end up making my own exhaust for the '2 I'll be using a Dynomax muffler.