I will have to disagree that they all do the "same thing". Please do not spend $10 on something that protects your brain.
i've shattered two helmets over the years. both times i got concussed. a helmet will NOT stop your brain from ping ponging around in your skull. and that's what damages your brain. it WILL help in preventing your head from getting split open.
Try this trick and spin it, yeah
Your head will collapse