Call me strange, but I put a very high value on protecting my eyesight. You could simply never practice shooting from compressed and retention postures and negate most of the risks, but that is poor training IMO since there stands a reasonably high chance you might have to do so if ever forced into using your carry weapon for personal defense.

Craig Douglas actually banned the ported Shield from his classes(which incorporate a lot of retention shooting) after having some potentially very dangerous incidents occurred....

10/21/17 ECQC Albuquerque, N.M.

As of... - Shivworks and Shivworks Alumni

Here’s a few quotes from some other well known instructors regarding using ported guns for defensive purposes....

“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 nor do I care for them on range training 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 have zero use for the comped Glocks. I have seen people injured from shooting them from retention and not getting the gun canted outboard enough before pulling the trigger.” - Chuck Haggard

“I do know one thing about the retention position. It sucks when one is using a ported gun!” - Marty Hayes