Completely guessing, but I wonder if they designed the "spoke" baffles to pinch in under the load and thus expel any stones that might fit between them, like a pebble squeezed between your two fingers and shooting out.
So about the same as a pebble that gets stuck in treads or kicked up by same? Definitely better than a bullet though just by nature of lower speed, what it's made of and because of its poor aerodynamics.
