I've got a couple of the LCT ones. I think they hold about 600+ bbs each and they aren't very expensive. Don't know if Fire Support has any left. If not keep an eye open for future restocks.
They look good and appear to be bomb proof (looks like steel to me) although I haven't played with them yet so I don't know how well they perform..
The CYMA C.84 fits my LCT LCK well; that's the 5.45/AK74 styled variety. You sometimes have to file off the wedge at the back a bit, also the pin on the front lip can be loose and if it comes out whilst the mag is in you might struggle to remove it. However if you get good ones or work around these issues they feed perfectly, are solid, look great, carry about 500 rounds each and are really cheap.