The tendency to tuck towards the landing gear during knife edge is rather frustrating on the 4* (you need to hold up to track straight). And an enlarged rudder would help it hold knife edge. I have the greatest possible throw on my rudder, and it still will barely hold knife edge for a few hundred feet, then it starts dropping.

I can do stall turns fine, but it requires a quick blip of throttle at the top, and you need to hold a little up elevator as well.

If I ever build the kit, I will lower the horizontal and add to the rudder.
Dennis-