High oscillation damping. Unlike a circle or a square, a five side object lacks point symmetry. In other words, in a pentagon, on the opposite side of a corner is an edge and opposite every edge is a corner. Regardless if the initial pendular impulse is towards a corner or an edge, the restoring force in a pentagon is clearly different. The pendular movement is disrupted and this dampens unwelcome oscillations, which in turn greatly reduces the risk of a hard impact.