I would look for a gear drive walk behind mower. I have one and there is no slippage at all because there are no belts! I pull a sulky with it and have never had a problem. Belt drive mowers dont have reverse, GEAR drive do. I am sure that I will get my head chewed off for posting this (big discussion on it ) But I would look for a complete gear drive mower. They have mow power to pull a sulky without burning through belts left and right.
The one that you posted is a belt drive mower, notice the things above the wheels in the rear, that is where the belt are for the wheels.
Complete gear drives dont have those belts it is just the trans straight to the wheels. Its a very cool system