[Integraguy1995]

Exhaust note is 97% in the muffler and/or resonator. You may notice a VERY slight change in sound, but I doubt it will be overly noticeable unless you are really listening for it.

Test pipe = one straight chunk of solid steel tube with flanges on the ends.

If your thing has any kind of honeycombing or holes inside, that's to allow gasses to flow into the space btween the inner and outer walls and through whatever may be in there. Some high flow cats are designed like that, but it's also possible that it's just a simple resonator designed to look like a cat to fool the random visual inspections some states do on their emissions tests.
Either case, it's not going to do much of anything to your exhaust note and our cars run so ridiculously clean anyways you don't have much to worry about.