If "all flying rudders" for LSA aircraft need up to 40% less area, what about "all flying elevators (stabilators)"?
Zenith gets away with the little All Flying Rudder without an anti-servo tab because the fuselage itself is used to provide sufficient fixed fin area for acceptable passive weathervaning. If you look at their designs they all have slab sided fuselages that are quite deep all the way back.  So there is a kind of "fin" with the rudder; it's just built into the fuselage.  I got to fly the Zenith 750 demonstrator once in Mexico Missouri and I recall that its yaw stability was perfectly acceptable even though the rudder just wanted to trail if if left it to do its own thing.

Horizontal tails have more work to do and horizontal surface area of the fuselage aft won't cut it without a fixed stabilizer surface; unless you use a stabilator/anti-servo tab. If you wanted to use an all-flying surface without an anti-servo tab, you have to have a means to "fix" the surface to provide stick free static stability.  If you're in an F-86, the all flying tail is hydraulically powered and can be fixed easily with a bungee that controls where the hydraulics wants to center the surface when you're not applying force.  Some gliders use all flying tails with no tabs of any kind, and they depend on bungee springs in the pitch control circuit to provide a tendency of the surface to want to hold a certain angle if you aren't hanging on to it.

You could design your ultralight with an all flying tail with no anti-servo tab by using a fairly stiff spring bungee as your "stick free" stabilization device, and for trim. You may find the anti-servo tab method provides better handling characteristics however and if it was me I would go that way.  

Note that airplanes sometimes use bungee springs in the rudder control circuit to provide a passive centering force that has the effect of increasing the fin area to improve passive weathervaning. Cessna 180/185s do this to improve yaw stability so that when fitted with floats they don't need extra ventral fins.  Problem is, it makes the rudder unpleasantly heavy.