Kevin,
Both of these augers do have a centrifugal clutch and they actually have the same clutch. I�m not sure it would be considered a slip clutch though. However If a rock is hit, the shock spring on the auger bit is designed to take the initial hit which would bog the engine down which in turn would cause the clutch to disengage. I would consider the dually if it is a very rocky area so that the force would be distributed between two people rather than just one person.