The function of a servo tab is very different from a balance tab.

With a servo tab control system movement of the pilot’s flight controls moves the servo tab.

The servo tab at the trailing edge of the main flying control surface produces a aerodynamic force to move the control surface.

The servo tab is displaced in the opposite direction in which the flight control surface moves. ie if you wish to pitch the aircraft nose up, servo tab is deflected down and moves the elevator up.

The system requires airflow from leading edge to trailing edge, when taxiing in a tailwind the effectiveness of this type of control is reduced.