I'm not trying to start an arguement here, but IMHO you sould never touch the prop once the glow plug is hot. The reason for this is because it's very easy for it to pop, kick back, or even actually start, and if the person isn't ready for it or doesn't have a good hold on the prop it could do some very serious damage to the hand. I teach all of my students that after the glow plug ignitor is attached the prop should be treated just as if it was running as it's possible to harm.

Ken