The Sig SE is a fun plane to fly... easy to if your rates are turned down. I have owned two and modified the rudder on both, I even added wing tip plates; however, it still doesn't knife edge well. Sure, it will hold a KE, but nothing like my other aerobatic planes. Still, I liked my SE so much that I have built a Sig SE from scratch scaled up to a six foot wing span, uses a YS140L for power and smoke... loads of fun.

About your question on counter balances, it is common on full scale to add mass and control area in front of the hinge line. IMO models typically should not have thier control surfaces mass balanced however adding control area in front of the hing line is fine.

Think about the loads on the control surface when it is moved. The airflow will try to push the surface back to neutral. The only thing holding the surface up (or down) is the servo. When you add area to a control surface in front of the hing line it too is pushed by the airflow; however, it is not being pushed back to neutral. Instead, it's pushed in the direction the control surface was moved. The next effect it that this assists the servo such that less torque is required to move the control surface.

I'm not sure what you mean by negated. Servo tabs do direct airflow so they are an effective part of the control surface. If you add more area in back of the hinge line you will need more area in front of the hinge line to offset the extra load caused by adding area in back of the hinge line... if that sentence made any sense. In that respect I supposed adding area to both kinda has a negated effect, but only with respect to the servo load. If you add more area to any control surface, be it behind or ahead of the hinge live, the surface will be more effective. In general, the rule of thumb I use is: Area in front of hinge line should not be greater than 25% of the area in back of the hinge line. As long as you stay at or below 25% you should be fine. Make you servo tab too big and bad things will happen.