Fortunately, because of where I work, I am able to avail myself of "samples" from industry reps on a somewhat regular basis.
Now that I have the Roni set up with a Glock 17, and a 9mm AR that takes Glock mags, I have been running the piss out of some aftermarket mags.
At this point, I am comfortable saying that I trust my life to the MagPul Glock mags, including their 27 rounder. I trust them just as much as the Glock factory mags, and infinitely more than KCI.
I have also been running the ETS brand Glock mags. Despite their translucent appearance, that unfortunately reminds me of Ramline Mags from the 80s, they have yet to fail me.
I am not ready to give the ultimate stamp of approval yet to the ETS mags, but, I trust them more than the KCI mags.
Not trying to pick on KCI, and I'm sure they can be made to run well, but, I feel we have better aftermarket choices nowadays.
Incidentally, my sweet spot for the rifle and the Roni are the MagPul 21 round mags. They will be in the guns when I need to participate in the unpleasantness. They are too handy. The size footprint is perfect for carrying or concealing those guns.