It's the self propel feature. You have 2 selp propel options with commercial WBs. Belt/gear drive is cheaper, but the belts that turn the wheels tend to slip in wet conditions, you steer with 2 brakes. Hydro WBs are a bit more expensive, but they are easier to operate and handle. plus they have a reverse instead of a belt drive with reverse assist.
start w/ belt drive, unless u can find a hydro for cheap.
Elite Lawn Team <------- Sold my business and now im an employee at CP Landscaping