I can't speak to shotgun barrel porting in general, but I can speak to the Vang Comp system. I have shot several of their modified tactical shotguns at Gunsite demos and had my own 590 done. Their system absolutely works and reduces felt recoil significantly, as well as reducing muzzle rise. I think they only do these for 870 and 590s though, and install the system for several LEAs nationwide. I suspect you are right about generic porting. I am not affiliated in any way with Vang Comp--just a customer.Shotgun barrel ports are a scam
It's absolutely not the same or even close to a rifle brake and shotguns run on barely 10 ksi of chamber pressure compared to the 55 ksi or more of rifles.