Like the title says.  Several months ago, I bought 8 30 rounders along with 8 10 rounders of another brand, all of which were a lot, including a bunch of ammo. Everything was new.

So, I crammed the 8 30's full today, thinking to do some shooting.  Let me just say these mags are absolutely THE most piss poor magazines I have had the misfortune of having
to deal with.  Oversized, wouldnt even lock up in the magwell, bolt couldnt even strip up a round, then when I decided to hell with them, I literally could not strip the rounds out
of them using the back of another cartridge, as they would just collide with the front of the mag.  Ended up having to grab the bullet end of a round and rotate it upwards to get the
ammo out of the mags one at a time. (SLOW)  Upon closer inspection, sure theyre stainless steel alright but the stock they are made from is thin, damn near as thin as two sheets
of notebook paper.  

I have read c-products mags in the same caliber are good, LOL, but this time Im buying 1 each of a few different kinds and testing before I go all in on 8 or 10 of them.

Korea is known for crap mags, regardless of platform. AR, AK, Glock whatever..if it is a mag and made in Korea it is almost gaurenteed to be trash.

I bought 3 RWB 30rd 7.62x39 AR mags a year or so ago.

Total garbage, won't feed a single round. Rims of cartridges get stuck on the ribs on the mag when trying to feed.
Tried brass case and steel nothing would function even a single round. Tried in AR's and bolt actions, junk.

RWB AK and Glock mags have been ok for me but I haven't bought any RWB after these AR mags.

For the AK, does that include the latest generation KCI 30 round mags and the KCI 2nd generation 20 round mags?

I think there's also SHK.

SHK makes some really nice all steel bodied AR 5.56 mags, CDNN used to run some killer sales.
KCI AK mags are thin steel but at least they're spec'd correctly, these and PMAGs are the only AK mags I've never had to file to fit in any of my AKs.

Never heard of RWB brand before but IMHO the Duramag 7.62x39 AR mags are the best, can't go wrong. That black teflon finish works well with poly coated steel case,
D&H also make an odd looking slab side 7.62x39 AR mag that works fine but has a pretty thick steel body so it's a snug fit.