It really depends on what you are shooting out of it. Like anything else that is ported the more stout the load the better the effect is. Porting a gun using light target loads probably won't make a big difference, however shooting magnum loads like turkey loads or high velocity slugs would probably be noticeable.
I had a mossberg that was ported, it sort of helped with recoil on heavier loads, but were I noticed a difference was in muzzle flip. It did a very good job of keeping my gun level with hard kicking shells.
They are bit on the loud side though.
Would I pay to have it done, nope, not at all. However I wouldn't let it sway my decision in buying a gun if I liked it.
There are better ways to tame recoil than porting in my opinion. Like a better recoil pad or added mass, or some kind of recoil absorption device.
Paul