I think a good quality plastic clevis would be fine for the 4 star. The only time I have had problems using metal screw on clevis' was when I put one on a metal carb arm on a magnum .52 four stroke. the vibration caused RF interference and I had no control at anything about half throttle. A metal screw on clevis attached to the plastic control horn at the tail of the plane should cause you no trouble at all. I think you will be fine with either choice.