A gravitational flipper does not use rubber bands, but a hinge. This means it will not close automatically and can be displayed more freely.
Actually, a gravity flipper does have a rubber band, but is designed to open by gravity (that is, does not need to be shaken or 'flicked' - will open up halfway if held be the edges, or by the fixed part of the insert). It will close by itself as does a conventional flipper.
No idea about a magnetic flipper; would assume that instead of rubber bands, it is just hinged, and uses a magnet to keep it closed.http://coingaffs.com/coingaff_shop/ds_gravity_flipper.html