Belt drive has a number of advantages:
No oil needed in primary case = no possibility of leaks from that area, and no need to regularly check/ top up.
Dry clutch plates have much higher torque capacity, so the spring pressure can be greatly reduced without causing slippage. This results in less stress on the fingers, the cable and the actuating mechanism. With the diaphragm spring, this is done by INCREASING the stack height.
Some belt drive kits offer a range of other ratios as well as the standard ratio. This is something you might want to check on your bike. Also, check if your brother fitted an oil seal to the clutch rod.
A higher (numerically lower) ratio is preferable IMO, because it gives higher overall gearing without the added stress on the mainshaft that a larger sprocket causes.
Another benefit is that kickstart effort is also reduced.
Why do you want to go back to a chain?
