Ive been using a lot of about 20 of KCI and KHAN Korean 9mm 17 mags on a weekly basis as range mags for about 10 years now. I also have around 15 or so of their 19 mags as well.
At this point, Id trust them as I would the factory Glock mags. I never had any troubles or issues with them, and they have been cycled constantly.
I did replace some of them with Wolff springs when I ran into some ejection issues, but that turned out to be worn out brass, and not the gun or mags. Im still shooting mags that are 10+ years old and are still on the original springs and they work fine.
I also have a few of their 33 rounders, and they have not been as reliable, and more prone to stoppages. I also have a bunch of factory Glock 33 rounders, and they havent been 100% either, but they do run better than the Korean 33 rounders.
This past fall, I bought a bunch of Korean 19 mags (I think it was at Gun Mag Warehouse) for $5 a mag, but they turned out to be another make than KCI when I got them. They function/shoot fine, but they will not drop free when empty. They do if there are some rounds left in them, but not empty. Just be aware if all they say is "Korean mags". They arent all made by KCI.