BTW, boost tabs look very much like trim tabs. In the case of boost tabs, they are driven opposite the direction you wish to move the surface. Their aerodynamic influence then drives the surface, or helps it move in the direction you want it to move. The spades actually cause a force that directly contradicts the resistance caused by the surface's movement. They create drag force opposite the drag the surface is causing that has been discovered to be "too much" for the pilot.

Spades can be a pita, as they restrict the surface's movement in one direction. And they can often create much more force in one direction than they create in the other. And who needs imbalance........... They appear to be a "duct tape and baling wire" solution to inappropriate design.