I always balance mine - usually with a trick I was shown back in my free-flight days. Hold the prop horizontal in one hand and in the other take a "T"pin and hold it up at a 45º angle and set the prop on the pin so the tip of the pin is halfway through the thickness of the prop in the shaft hole. Let go of the prop and the heavy side will drop. Scrape the backside of the prop with a knifeblade on the heavy side. Repeat until it stays level. I have done 20" props with this method and it works as well as with 6" ones.