The pro's of the gun speak for themselves, great externals, some quality internals, but I'll hit you up with some of the serious cons of G&P guns:
G&P gears are natorious for shattering shafts. I've had two come in for repairs with broken shafts, a third with a broken gear teeth, none from any jams or anything like that.
G&P's white piston seems to be hit or miss. I've adjusted the Angle of Engagement on a fair number of them and they run strong, yet in an equal number that I do the AoE mod to come back with broken pistons. The old G&P white pistons are far too hard and break really easily.
G&P's Deans connectors suck, they are looser than a prostitute and really are not made of that good of quality plastic or metal. Their hop up rubbers still suck balls compared to aftermarket, but at least their hop up units dont suck as bad anymore.
Good purchase if you dont mind replacing stuff when it breaks. Most of the rest of the internals are bullet proof.