Some people say it's good and some say it does nothing. I lean to the nothing people.
Shotguns operate at much lower pressures(12,000psi) than a rifle(50,000psi), and venting off some of the powder gas won't do much help in controling recoil.
In rifles part of the recoil impulse is from the jet/rocket effect from the gas comming from the muzzle, and a brake will help control recoil. Shotguns the recoil impulse is more form the fact you are shooting a 492 grain hunk of lead out the barrel.
The porting makes the gun sound louder (venting gas closer to shooter) and some think the ports/holes look cool.