Ultra high crank case compression, Fan cooling over a cast iron cylinder, and indestructible clutch/transmission.
The 'N' engines have more aggressive porting, larger heads, and generally roller bearing little ends.
The reason most people Love them is because you can jam blue scooter springs into the clutch, a polini 80 kit, a pipe from just about anything, Regear and go 50 Forever. The build quality on the engine is Stellar and they're easy to work on.
The V1L engines have a shorter stroke, they're case inducted, and a lot of them come as kickstart engines. A lot more in terms of kit availability.