Those sand guys use huge paddles as tyres and so produce lots of grip even on sand.
He wrote "off road" not "sand" and it's not necessarily the same. Anyway, paddles or not, it's not the traction that kills gearboxes in off road application but shock loads they get at all those jumps, holes, gear changes, heavy tires etc. So the question is what will be your driving style - you can get away with beefed up beetle trans on the road if you use it properly/gently or you can destroy a mendy with stupid driving. My advice -get the strongest gearbox you can afford.