Those are trim tabs. They are used to keep the blades in the same tip path plane by turning the blade into a reflexed aerofoil (where the mean camber crosses the chord line) to counteract twisting moments as the blade changes ange of attack. In other words they can introduce a nose down moment to oppose a nose up one and vice versa. The BERP blade does the same thing aerodynamically. The idea is to preserve the blade's integrity.
If that was a Kaman it would be part of the flying controls.
Phil