For: UK Arms 2500rd M4/M16 High Capacity AEG C-Mag (Motorized)Having owned a CA M15A4 and TSD M4 Tactical, and having used and reviewed both a TM M16A2, and an Echo-1 M4 over the last six years, I would say that I'm quite well-versed in the AirSoft rendition of the ArmaLite 5.56mm rifle.
I've also used lots and lots of different magazines; some quite good, and some not quite so good.
The UK Arms C-mag is so bad that it doesn't even deserve to be called "not-quite-so-good". In fact, I would go as far as to say it's downright bad.
This is coming from a guy who can compare the Echo-1 M16 to his own SystemA/G&P rebuilt Classic Army gun in a positive light, so please don't think I'm being an elitist jerk when I say that this magazine is a waste of $50 dollars that you could spend on two 300-round hicaps.
The UK Arms C-mag is a slightly cheaper rebadged version of the AIM "S" twin-coil C-magazine also marketed by AirSoft GI. THe magazine's body is comparable to any of the top-shelf guns, but that's where the similarities end.
The pigtail switch has serious connection issues. If you unplug it too many times, the connection point will break away from the magazine inside, and then you're quite out of luck, since this is the only way to wind the magazine. THis is a rather nice problem, compared to, say, the fact that the high-cap loading mechanism used inside could have seen serious improvement if you were to hand out a few dozen to teething third-world babies to gnaw on.
I'm not exaggerating one bit when I say that the magazine's mechanics were assembled half-backwards from shoddy parts, with crooked springs installed in the wrong places, and gears that don't quite grip eachother, a battery container that doesn't have anywhere to go inside, and a highcap mechanism that's glued together, not even screwed together, so you can't take it apart to repair even if you wanted to.
If you have the time and money to spend, you might try adapting this magazine to the internals from another high-capacity magazine, though to be honest, the thing was so poorly assembled that I couldn't even tell you which kid of magazine to use.
Mine didn't even make it through 30 rounds, and the place I bought it from gave me a real hassle in returning it.
If you really must try your luck, PLEASE buy it from here. Not only will the price be better, but AirSoft GI's fantastic customer service will take much better care of you than Evike's staff, when this magazine inevitably fails.