But, If (the big if) the mechanical part of the flying stab could be made with nice bearing and a proper pivot point that didn't have slop, etc. then they would be better because the problem of incidence setup goes away. What ever the angular relationship you end up with is would be good for that airplane. I think the all flying tail would be lower drag (both creating the same lift and pitching moment) than a flapped (which is what a horizontal/elevator is) surface making the same lift, but, I don't have the numbers in front of me at present.

Actually they are just as effective as a regular stab. Think of the system with a 10 percent chord elevator. You get a certain pitching moment with elevator deflection and is good enough for a lot of airplanes. As the percentage of chord of the elevator is increased the pitching moment at the same deflection angle is increased until you get the percentage chord to be 100 percent. The pitching moment with percent chord always increases although the increase might not be linear.

But the problem is indeed with the mechanical aspects of the system. When I think of the workmanship I have seen at the average flying field being aimed at a flying stab installation it makes me very nervous. At least with an elevator you can look and seep pretty quickly if the thing has been knocked out of alignment and especially so if there is some aero balance in the design. Not so with the all flying stab.