It's light force over time causing expansion. I don't know if anyone has ever used it, but could we get a testimonial from people who have? Expanders are painful and forceful, but this thing doesn't seem like it's meant to apply that much force - in fact its expansion is by the heat of the mouth so that must be very light force. Even less than the tongue generates.
If ALF works, mewing must work too?!
Sorry for two topics at once