I've been running the mock-up kit on my truck for a little over a month since we put my stock turbos back on so we could copy the single turbo kit for production. Been working flawlessly and helped with the drive pressures at wide open throttle. We dumped it to atmosphere looking for ease of installation and cost effectiveness. Much easier for someone to install when there is no need to mess with the downpipe (removing it, drilling, welding, etc...)
We were afraid the soot and sound would be an issue like you've mentioned, but the way we've got the gate set, it is really only coming open at wot and by then the truck is already running pretty clean out the pipe, so my truck really hasn't created much of a soot mess underneath. As for the sound, it makes a pretty distinct sound with the window down and outside the vehicle. With the windows up inside the cab it sounds more like a broken manifold bolt, like a ticking. But I towed 14,000lbs two weekends ago and it never came open while towing at it's current setting on the regulator. Under normal driving conditions it stays closed, only opens when you get after it hard.
This may not be the kit for everybody, but we wanted to offer a mosre cost effective and easier to install system, this is what we came up with. Just about as simple and effective as you can make a wastegate system. Plus, with retaining the crossover pipe from the up-pipe and mounting the gate next to the driver side manifold where the cooler was, you can still use the stock back pressure sensor in the factory location.