I've recently got a G&P M16, need a high mAh battery though.
My 1600mAh 8.4v got extremely hot and for some reason made the gearbox lock etc.
I took it back, Fire Support replaced the cut off lever with a Systema one and I bought an 8.4v, 3700mAh battery - works great now, amazing trigger response and ROF!
Externals are good, solid and have good finish on them - nothing too rough or too shiny.