I have a ported .40 S&W 99C. Had I known what I know now before I sent it off to Magnaport, I'd have not done it.
They did a great job. It is beautifully done. I enjoy the weapon at the range.
The benefit of the ports is so marginal in terms of recoil that I think it is outweighed by the disadvantages.
I have not shot it from retention, but it is easy to see how that would create a problem if the gun was really pulled in tight against the hip or chest.
I do not think flash is going to be any issue at all, so my main concern is shooting from retention. The way it is ported, the flash is off to the sides and not in the center field of vision.
I do not generally use it for carry, and one of these days I am going to sell it and get an XD9 SC or another 9 mm.