I read this in another forum -

The gear box included in this kit is NOT the same as the Grubee gear box. Grubee actually has a patent on his design. The HuaSheng engine output shaft is too short for this gear box clutch design. This means that you have to use several flat washers to make the shaft longer. This is causing the bell housing to split and fail after a short amount of use.
2) The gearbox is not compatible with the Honda GXH 50.
3) The gearbox does not include an engager system.
4) The gearbox includes a fixed rather than a freewheel output sprocket.
5) The kits are sold with no warranty from the factory. This means it is up to the vendor to stand behind their product. I tried to follow the instructions to submit a warranty issue with one of the vendors and the web form I was supposed to use did not exist.
6) To my knowledge there is currently no way to obtain parts for this kit. If you break something I guess you’ll need to buy a whole new kit.
7) The mounting plate is not adjustable which limits the bikes the kit will fit.
8) Does not include the dual brake, throttle, kill switch grip.
9) Does not include a kill switch. You must purchase and install your own.