I have two all metal JG's (Jing Gong) and they are both awesome!
JG - MP5 Navy
Jing Gong - W4 S-System Carbine
They are both later versions of these models, and I have never had any trouble with.
I did own a very early version of the JG MP5 which was mostly plastic, and it wasn't very good at all.
As long as you go with one of the all metal versions, I think that you will be very happy, I know I am! :tup: