@RAT 5, to be honest, as far as i know it is not approved for single autopilot autoland. It is a non-documented "feature". We never trained its use as we always use two autopilots on approach anyway, even if a manual landing is planned.
Someone mentioned above it would be better for a low disconnect height as in single autopilot operation there is no backtrim. That may be, however if trained for the backtrim it is a non issue to be honest. Same as the kick in the rudder during a single engine go around once another roll mode is activated.