In 'conservative/hands-off my guns' ID they have a law that makes modified exhausts illegal. That's part of the reason for the twin-tip - it still looks mostly stock.
The downpipe was a pain - had to enlarge all the mouth bolt holes and, since I have a AT trans, 'modify' the pipe near the trans hanger. But the hanger worked w/the stock location after a little modding - I just connected it by one bolt on the tranny side, rather than both. The good news was that the DP had the bung for the O2 in the stock location, and has another near the other end, if needed (wideband?). And the downpipe perfectly connected to the rest of the stock exhaust.
A local shop took the 3" midpipe I brought (was on a WRX), put in the cat, built a pipe for the axle back (not mandrel bent) and stuck on the muffler.
Sound? Noticeably louder, which isn't what I was after, so not sure it's going to be a long-term answer. I really don't want to attract attention - not my style. The sound isn't intrusive while cruising and doesn't really become an issue 'til 3K RPM which is below 70MPH, but it's loud @ idle in the a.m. while warming up. And @ WOT it may not wake the dead, but make 'em turn over. I've had it installed for a couple of months and decided to add a resonator, but it made little to no difference. My guess is it wasn't long enough (only 12") to help, but that was all I had room for.
Performance? I'm not sure it spools that much sooner (some see full boost <2K RPM!), but it's flows to redline faster and easier.... and seems to not want to stop @ 6500. The TCU/Rev limiter kicks in and it shifts before it runs out of breath. Overall it's a noticeable improvement over the stock system.
A couple of other notes...on my TD04 (never had this connected to a VF11), I was getting 12-13 psi (hitting fuel-cut on occasion) before I installed the Revtronix chip, even though the wastegate actuator is 10 psi. This may be boost creep caused by the larger exhaust and larger displacement EJ22T vs. the WRX's EJ20. Stock WRX exhaust is 2.25", I believe.
Downpipe:
Resonator:
