The servo-operated tab in the photo is not a boost tab, but a servo tab. Servo tabs are vastly more effective than boost tabs, but they are more complicated, and require good static balance of the control surface. Boost tabs are passive devices that deflect in response to control surface movement. Servo tabs move the free-hinged, weathervaning control surface directly. Some full-scale airplanes use both - the DC-9, for example, requires no hydraulic boost on its ailerons and elevators. The pilot moves the servo tabs on the trailing edges of the ailerons and elevators by cables connected directly to the control column, and the boost tabs greatly reduce the force required from the servo tabs.

The result is an amplification of control force that may easily exceed 100 times. Normal R/C servos could probably exert sufficient torque to control many light aircraft, in case anyone has a yen for really gigantic models, by a combination of servo tabs and boost tabs. Incidentally, boost tabs are sometimes called balance tabs.