These work find in my JG G36k, I recommend them to anyone looking for extra magazines. They are thick plastic, do not creak or flex, and are flat black (not shiny looking).
The only reason I gave them a 4 instead of a 5 rating is because they are a very snug fit in my particular gun, while the stock magazine fits much better.
Stacks well (good thing since they are difficult to get in and out of magazine pouches)
Did not notice any poor workmanship anywhere on magazines.
Metal BB release for easy unloading of magazines.
Very cheap for 5 magazines, I remember paying about $35 a few years ago for a single low-cap magazine.
Magazines are fat, very tight fit in my single mag pouches (not King Arms fault, just the design of the G36 magazines in general).
Very tight fit in my JG G36k magazine well, I have to slap them in to ensure they are properly seated after inserting them.
My stock hi-cap magazine slides in and out very easily, I may try to sand the upper portion down on these.
Rating: [4 of 5 Stars!]