I'm loathe to enter into this, but a true stabilator without the anti-servo tab is unstable. They are designed with the centre of pressure ahead of the hinge line, and the antiservo tab is the only thing which stops the stabilator from diverging to one of the control stops. Quite often the final design does not quite mirror the theory, usually due to the tailplane centre of pressure not agreeing with theory. Theoretically a stabilator requires less surface area to provide the same overall static stability than a fixed (or trimmable) tailplane and elevator, but can have some nasty dynamic characteristics.