I know the Suzukis (not sure about the other Japenese scooters) are shaft drive. Nothing to adjust, no replacement, just change the final drive oil every once in awhile... I'd take a drive shaft over a chain (even sealed) anyday...
Just like a shaft drive unit, BMW will want that chain oil serviced/changed. Most likely it'd take considerably more fluid/time than a shaft. My FJR might take 1/3 of a quart to change the final drive unit...
The original Honda 50 step thru scooters had an auto clutch, 3 speeds and SEALED CHAIN Drives...
BMW is known for their drives shafts, very surprising....