On a range, target or competition gun, I don't really see it being an issue at all. However, on a defense weapon, I think it's a feature best avoided.
Considering the vast majority of civilian self-defense encounters occur at close-quarters, the probability of firing from some type of retention position being the best tactic is relatively high. In a defense situation, I want as much of the blast as possible directed into or toward my assailant and all the bullet velocity I can get, especially with a snub revolver.
There is pretty much a consensus of thought on this issue among reputable instructors. I'm not aware of a single respected trainer that thinks firing a ported gun from retention is a good idea or feels the risks are negligible.
The biggest negative thing I see with the porting is that if you have to fire from a retention position, it will blast hot gases and debris up toward your eyes. That's not just a distraction; it could cause permanent vision damage, and at the worst possible time. - Massad Ayoob
I don’t like ported barrels on self-defense guns. The clearest danger is the risk of hot, explosive gases vented up into the shooters eyes and face. - Michael de Bethencourt
Ported barrels can be downright dangerous when fired from retention. I have personally seen where what appeared to be part of the jacket embed itself into the face of one of our officers during retention training. Even if no hard particles leave the port, the gas definitely is directed straight into your face.- Mike Moore, Gunsite Academy Instructor
I do know one thing about the retention position. It sucks when one is using a ported gun!!! - Marty Hayes