KCI mags have worked in my G17 without issue.
They are obviously much cheaper quality wise and a bit more stiff when it comes to loading but they do work. At least all mine have. The 17 and 33 round mags.
This has been my experiance as well. Bought a bunch of KCI Mags for range use 10 years ago, have yet to kill one. Classic Firearms regularly has their 33 round mags for $10, bought some on a whim and they have been great ( figured three for less than the price of one OEM mag was worth the gamble )
The Korean military uses Glocks and Glock set up their plants, so I tend to trust these a little more than other aftermarket ( I do have some Magpul, which are OK )...that being said, OE Glock goes in the carry gun.