You guys raise a good point on the ability of such engines to totally destroy the whole front of the model in a blink. Ideally the engine and prop would be mounted to a solid test stand and the runups done on the stand well away from the rest of the folks in the pits. And the engine only advanced to full throttle once standing safely behind the stand and reaching foward gingerly...

One should not in any way underestimate the power of prop blades of that size. They could easily cause serious injury or even death at closer range.