The difference is in the density of the foam used in the padding. the $3.50 piece is for non-lethal areas. i.e-legs, arms, noiwhere near the head. The $24 piece? you guessed it! around everone's noggins. It's about the same difference as riding a motorcycle with a batters helmet or a motorcyle helmet.
Matt- headin' fer the noodle isle a wallyworld