IronEagle, the period you are referring to was when the tab ideas were developed. I think even some of the late WW1 airplanes were using adjustable tailplanes, certainly many had offset fins to counter yaw trim. Fokker pilots were known to carry a bit of U/C bungee to assist with elevator trim...So far as what the difference is between a balance and servo tab is, I think, and only think, that a balance tab is operated by the surface movement, whereas the servo tab is the pilot operated device, which then moves the surface. My own experience is that models, generally, have no need of the things other than reproduction on a scale model, as we have a rigid, servo operated system with a rigid trim system, in other words, the tab is physically unable to do what it was originally intended.
Evan, WB #12.