Performance wise, they most likely won't be a benefit. If you have a deep breathing engine that moves some serious air, and you have a corked up stock exhaust, with a halfway clogged cat... Then a dump will help you.
If you're like most of us, don't have a cat, and have upgraded the exhaust any, a dump really won't do much. Other than sound BADASS when you want it to.
The easiest way to tell if a dump helps is to look at the spool time on a powerlogger. Although sometimes faster spool can go from hooking, to knocking the tires loose. That result is slower times, but a nice pretty sideways rolling burnout!
In your case, since you have a test pipe, there's a little more to it, that just bolting on the dump valve. You'll need something to hook it to. If you have welding skills, it's not too hard to cut and add a dump tube. If you don't have welding skills, you'll need to buy a wye that is set up for the dump and a couple band clamps.
I have both if your'e interested... A 3" dump tube and an electric dump with a wireless remote.