"Bought a couple of these during a magazine sale as "disposable" mags. Despite Cyma's reputation as a cheap product, their magazines are surprisingly good mechanically. Exterior finish is a bit rough (rough seams, matt black finish is spray painted a bit unevenly), but if you're a stickler for fine details you can fill the seams in with super glue, sand the seams flush and repaint.
The followers are u-shaped vs the conventional nub that helps feed the rounds more consistently. I took them out on a game earlier in the year and managed to use all 10 magazines without any feed issues in my Echo1 AK700, once they were broken in (see below).
Note to new users - the magazines need to be broken in. Put in 1-2 drops of 10w silicone oil into the feed nozzle, and run some cheap bbs through it 2-3 times. The magazine will be tight the first few times so you'll be able to feed in 80-100 at most. Once it's filled to capacity, leave the rounds in overnight then get rid of them the next day by releasing the BB retainer (do not fire them!). I tend to buy a cheap bottle of bright orange ones so I know that they are only to be used to break in a magazine."