This is a well designed mag. Well, I guess it has to be, since it's the only one made for the WE M4. Maybe some aftermarket company will step up and make something really cool like a Pmag sleeve to fit the internals into.
Anyway, as a testiment to WE's attention to detail, their mag has the EXACT same dimensions as a real USGI 30rd mag. As I compared the WE mag with the real steal, I found that its shell was created the same way as the real one - even having the same number of spot welds along the seams. Heck, the only thing preventing the real one catching in the magwell of the gun are the retainer tabs which hold the rounds in. Really cool stuff. The only place it was lacking(aside from the obvious top section) was the floor plate. There's no stamping on the WE version, but guess what? The floor plate from a real steel mag is a direct fit! So there's a tip for all of you guys who absolutely have to have the most realistic looking equipment.
As far as functionality, well....mine haven't failed me yet.
In short - buy these mags for your WE M4! Otherwise...you won't have mags.
-True real steel dimensions.
-Well made and weighs about the same as a fully loaded 30 rounder.
-Reliable. Just keep them lubed. The seals on a gas or pneumatic gun are EVERYTHING.
I would list the price as a con, but this is an expensive hobby. Sure, you can get an AEG mag for around $11, but the difference in cost between an electric gun and a gas one are offset in different areas.