Just received this gun today. First impressions, gun felt really solid, and quite heavy, almost as heavy as my full metal A&K M16. It definitely differs in that it's obviously shorter as it's an M4. Easy to grip, and aim around. Very VERY solid feel, no strange squeaks or anything.
Quick runthrough of the gun externals from front to back: the outer suppressor is metal, and extends to about halfway back in the front handgrip, so overall about 6-7 inches long, not just the 2 or 3 inches that stick out the end. Front handgrip is also full metal, and looks great even with all the accessories off. One thing I would warn to people buying it; the screws are a 2.5mm hex head, and I did strip out one of my cheap allen wrenches on it. I have no worries about stripping out the threads on the handgrip though, as it's very high quality metal. The connection between the reciever and grip is solid, no wobble whatsoever. Body is very good for being a polymer body, only complaint is that the dust cover WILL open due to very slight body flex, but you can only see it if really squint. If you're that concerned about it, spring for a full metal body, but for me, it's very good. Magwell holds and feeds from all my preexisting mags, slight amount of extra room in mags, but I've never had one that holds mags tight. My favorite thing is that it's not a standard M4 pistol grip, it's smooth. No little nub to get in the way of my finger, which drives me absolutely nuts with my M16. Finally, on to the crane stock. Solid. Slight bit of flex if I want to complain about anything. Hard to figure out how to open the first time, but once you get it, super simple.
Internally, the gun is silky smooth. Blowback feature is very cool. Charging handle is smooth to pull back, and made of metal. Hop up adjustment is easy. I have the Tenergy 9.6V crane stock battery, and it not only fits flawlessly, but runs through ammo like no other. Watching bb's in light at night, it's almost a solid line, much higher rate of fire than my old gun. Semi auto works, so that's certainly an upgrade from the old gun. Gears feel very smoothly meshed, and the gun doesn't feel like gears have to work hard to shoot. I'll open it up soon to check it out, and I'll post a follow up on that. Haven't had a chance to chrono it yet, but I'd imagine it's near the higher end of what ASGI says, probably around 330-340. If I can edit this, I'll report back with findings later.
Quick bit about the front handgrip: It comes with 10 pieces, 2 handguards, 2 side rails, 1 long top/bottom, 1 short top/bottom rail, a full length riser piece, 2 'mock' short length rails (look like rails and are ribbed at approximately the same interval, but don't work as rails), and 1 45 degree rail (mounts to one side, and the rail is 45 degrees over from where it mounts). Comes with plenty of extra hex bolts, probably about 2 dozen or so don't worry about losing them as there are replacements. Only complaint about it is what I noted earlier, some of the bolts are WAY too tight, and may damage cheap allen wrenches
-Shoots very quickly with a 9.6V battery
-Good crane stock, easy to get into but still solid
-Modular rail system for however many accessories you have
-Cool looking, everyone always takes a second look at it when I show them
-Solid feeling fire selector
-Non-standard pistol grip
-Great internal job done by G&G and ASGI
-No iron sights (not a bummer for me, I had a red dot I wanted to put on it anyway)
-Plastic body (But a very high quality one at that)