Although I haven't used these in a battle yet, I can tell that these magazines are of very high build quality. They are heavy because of the full metal external construction. The paint seems to be thick and will be very difficult to chip. I haven't filled up the magazines yet, but I wouldn't necessarily consider filling them up to the full 190. Not only will you be more likely to waste ammunition, but it could over-tension the spring and shorten the mags life or cause feeding problems. I'd say go for about 90-100 BB's or basically a full speed-loader into each mag. When you pick them up, they are solid as a rock, and make next to no noise when shaken, hinting at nice, tight, well built internals. They are a nice, tight fit in my Echo 1 M16A4, and they will definitely come in handy in my next battle. Yes they are expensive, but I think it's worth it for the amazing quality.
Oh, and before you do fill your magazines, especially mid caps, spray some silicon lubricant down into the spring tube, just so it doesn't stick when feeding.
I'll do another review on these after having tested them in a battle or two.
-Solid metal externals, minus top and bottom plates (like any other mag)
-Equally solid internals (judging by weight and lack of noise when shaken)
-Paint (thick, seems durable
-Large capacity (if you choose to fill them up all the way)
-Fits great in an Echo 1, so it will probably fit in most other M16's/M4's/whatever else takes these mags
-They're mid caps, no winding wheel or butterfly key, just pop them in and go!
-Not exactly a con: Although the picture sort of makes it look like they are black but with funny lighting, they are in fact a darkish gray. If you have ever seen the Noveske high capacity mags, these are just a slightly darker shade of gray. This isn't really a con, and I personally like the color, but if you really want to you could just paint them black. If you really hate gray mags, these aren't for you.
-Also not really a con but if your on a budget, these are pretty expensive compared to the other mag packs on this site. I personally would have just gone with the Echo 1's or A&K's, had they not been out of stock. But, I'm assuming that the extra high price is for the quality. These things are built like bricks!