My understanding of the primary advantage of ported barrels is to compensate for tendency of barrels to rise upon firing and thus keeping barrels "flat" for quick and more accurate second shot. I personally like them for O/U guns. Since porting is at end of barrel, there could not be any meaningful loss of velocity. Friends do claim my guns seem loud. I wear plugs + muffs and don't notice any difference. A competitive advantage perhaps?

A Springer Spaniel, a 6# double and a fair day to hunt.