There's no telling how effective these things are, since they have never been tested. Thy also produce pretty weak energy levels, which may or may no be enough to disrupt the hair cycle and make the hair fall out.
Even if the hair does fall out, it's highly unlikely the energy emitted by one of these will cause anything more than a temporary hair removal.
They don't really hurt, but they do take a long time to treat each area. It would take a couple of days at least to treat your legs with one of these.