For: JG T3-K1 AEG Airsoft GunThis is a good, solid gun. I'll go over specifics and then give an overall Pro/Con:
Good weight, but it may get heavy carrying around for a day. At least it doesn't feel cheap. Just get a good sling.
As for the build, it feels solid to me. I haven't held the TM SG1 which I heard creaks like a mother, but this gun really does not creak when is is carried or shouldered, even though it is so long. There must be a metal frame in the foregrip. I am really impressed. Negligible wobble anywhere. I've had a good number of full stock guns where the stock feels like it is about to snap off. Not here.
Not much external metal though. Doesn't bother me. The metal parts are the outer barrel, bipod and bipod hinge, rear sight, sling mounts, trigger, front sight, mag release, charging handle, and stock mount (not the stock itself, but the piece that attaches the stock to the receiver).
The finish is what it is supposed to be, but (personally) I don't like how the receiver is a lighter gray than the black foregrip and stock and pistol grip... That is how most SG1s are, though, so... Also, the top of the receiver feels a little on the cheap side, but it doesn't feel like it could break.
Mags are metal, ~500 rounds, and fit well. (comes with a mag wind key) Selector switch feels plasticky, but clicks into place nicely. Bipod is sturdy when the screws are tight, but after an hour of skirmishing there was some wobble when folded to the foregrip. When I had a chance, I just tightened some external screws with a flat-head screwdriver and it was fine again.
ROF is decent with the stock battery, but the battery itself doesn't last long (1500 mAh NiCad). Buy a better battery. FPS is fine. Accuracy is good for the stock barrel, but can really shine with a tightbore. Hop is what you'd expect from a JG. Upgrade with a TM hopup for better range/accuracy.
Accuracy (potential as well)
Good metal mags
Important outer pieces are metal
Very little wobbling/creaking
Some cheap feeling plastic parts.
Visible seams and weird weld-like seams in plastic (rare)
Bipod can get loose
Awkward in CQB (duh)
Stock battery (it works, but...)
So, if you want a decent stock long range support weapon or an upgradeable sniper base on a budget, this is your gun. I'd give it a 4.6, but since that doesn't exist, I'll round up.