Well first off, a disclamer. I don't own any GI custom guns, so this is all from useing them, research, friends, and sales reps (that own them).
The are all OEM guns, with aftermarket rails, and possibly outer barrels, iron sights. The extra price is pretty much for the $50-$125 rail.
The OEMs are G&G, lonex, and VFC.
My thoughts on them.
The G&Gs aren't worth it really, put a $120 rail on a $140 gun?
VFCs, I don't know much about them…
Lonex, I really like these. First off I was responsible for this one
http://www.airsoftgi.com/product_info.p ... s_id=16319 And I would recommend it very much. They're acceptable internally (I normally upgrade most everything in KWAs), the motors are aftermarket A3s, gears are good stock, spur gear is self shimming, Ball bearing spring guide, ORING AIR NOZZEL, 8mm bushings, very nice ported cylinder, polymer piston with several metal teath, ported piston head, wireing could be better (so could most), and generally good parts otherwise.
Externally, it's all opinion, however in mine they're quite good. Comes with a flash mag.
Thank you,
Airsoftee
Who's there? Oh, just me.
But you should know, I never travel alone…