That's not a new sense, just using the existing tactile system with a magnet.
If they would restore vision by using e.g. the cochlear nerve, that would be something.
I've heard about people experimenting by wearing a belt with dozens of haptic motors and a compass, so that it always indicates the direction of north. After a while wearing it, they stop consciously feeling the sensation of the vibration, and just feel "northness". And then when they take off the belt, they feel weirdly disoriented for a while, even in familiar places.