Seems perfectly safe to me, centrifugal forces are going to keep you in your seat unless you deliberately push yourself out at which case it's just as dangerous as running under a seesaw or into a swing.
They're awesome! You can easily get them so fast that the centrifugal force pressing you towards the poles in your back starts to hurt your flesh, and you wish you were alone on it so you could stop this madness. huuuuuuuuuuuiiiiiiiiiiiiiiiiiiiiiiiiiiii