Look at some of the current pattern airplane designs. Some have rudders that have a TE that is close to an inch thick. Reasons for this is that the additional drag helps the airplane track, Gives better response around neutral and is more powerful at slow speeds. I once had a 45" Katana electric aerobatic airplane that was very pitch sensitive. I glued on 1/2" strips of depron 3mm thick top and bottom of the stab LE. The pitch sensitivity went away. The tubulence caused by the strips kept the airflow attached to the stab and made the airplane more stable. Carden aircraft designs their airplanes with thick trailing edges because it makes the surface more effective. In full scale it [sharp TEs] will increase efficiency and of course that is important to save fuel costs but us R/C guys don't care about that unless its a pylon racer or sailplane.

In a nut shell, you will gain more stability and surface effectiveness on a small model by leaving them square.
<br type="_moz" />