I've worked on a million G&G top techs.
-Solid internals inside gearbox (not gearbox itself) for a stock gun, quite reliable
-Pretty good motor for a stock gun.
-Best looking bolt movement on AEG
-Accurate for a stock gun
-Gearbox shell is proprietary and EXTREMELY brittle, always cracks at the front
-Pneumatic blowback is EXTREMELY damaging to the brittle gearbox, introduces massive air leaks and require much heavier springs. Paired with the terrible mechbox shell this I see cracked gearboxes more often than stripped pistons from G&G PBBs.
Guardians of Asgaard - KF32
VFC H&K 416C
VFC KAC SR16 JL Billet SBR
TM FN Five-seveN