Well, I'll pile on this thread. I've generally avoided really harping on Stillen negatively very hard, because I think they *do* put some quality stuff, and I have had some nice interactions with some of the guys there, especially Josh (who was/is a frequent poster here) back in 2009.
I've had so many bad experiences with so many car parts vendors over the years, I'm kinda at my limit. It seems like the whole industry sucks, and I'm just getting a little bit tired of how we, as aftermarket car parts consumers, tend to hold them to a lower standard and just accept it.
I've had two issues with Stillen and my 370Z over time, which I'll recap here:
The first was their ridiculous first-generation catback exhaust back in 2009. I spent untold time and money on that piece of ****, running around to different exhaust shops having them try to fix it, all the while Stillen's getting the early marketing benefit from me being an early adopter (at full retail price!), and telling me their exhaust is perfect and it has to be an install problem. Then they finally announce a "minor design update" to correct the fitment issue. Just before this, one of my frustrated exhaust shops made a new bend in one of the pipes to try to work-around the problem. That bend ended up leading to a persistent leak problem at a nearby flange. Stillen didn't want the installer-damaged exhaust back and didn't want to give any kind of refund. I ended up throwing the whole catback in the trash and buying Fast Intentions in the end.
So figure the whole cost of the Stillen cat-back, my time doing the initial install, my time trying to fix and re-installing it a couple of times, my money spent at two different exhaust shops on labor trying to fix it, me buying custom gaskets trying to fix it. All of that and in the end it just goes in the trash as unusable and no compensation. I sure as hell wasn't going to pay retail for a replacement from the same guys.
The other incident came along when I bought their 7AT cooler kit, stupidly. The gist of the incident is documented
in this post, but the bottom line is the lines were too large for the factory fittings, and I wasn't about to take that sort of increased risk of an ATF cooler line blowing off during hard usage from improper use of clamps on an oversized hose. I emailed them about the issue twice two days apart and *never* got a response in the ~9 months since. I ended up basically just re-using their Setrab core and making my own fittings/hoses kit that I sourced myself. What a waste of time and money - I basically paid them to put a kit together and validate it, and ended up only using the core from their kit and putting together my own validated hose/connector setup. As far as I know they're still selling people the same kit, and I'd imagine most installers just follow the directions and don't think twice. I'd be wary of running this kit if I were you.
It's doubtful I'd ever buy another product from them again.