Lots of rumors swirling about these mags these days since they're readily available so I'll try to sum up what I've found with them to date......
-In terms of reliability, they function flawlessly in all rifles they've been used in to date
-Come in 10, 20, 30, and 40 round capacity
-Nice even finish
-Made out of steel. I'm not really a metal magazine AR fan but I think steel mitigates some of the issues the aluminum USGI mags are known for (spread feed lips, denting, ect...)
-Insert fully loaded and drop free in my Colt LE6920
-Cost. The 30 rounders are $18.70 and have free shipping if you order 6 or more.
-The overall construction seems pretty good. Nice welds, finish, ect...
-Unmodified, they were difficult to insert on a closed bolt when fully loaded in several rifles. They were extremely difficult to release after insertion when fully loaded. All mags tested were fully loaded for over a week before testing.
-They're heavier than other competitor's mags (USGI/PMag/Lancer/ect...)
Once I took off about 1/16-1/8'' from the mag catch in the mags (see the end of the video below) they functioned just fine in every way in all the rifles I've tried them in. All in all---I'd be more concerned if they didn't work than the fact that they had to be slightly modified to drop free so that's a good thing but I'd prefer not having to tinker with mags to get them to function in my rifles...
If you just need to get a hold of some 30 rounders there's certainly worse mags out there (Promag for example--they're selling at the same price these days as well).
Here's the video showing a little shooting and demonstrating the things I talked about above: