These have been all the rage. As far as I can see, the trick is that if you get it spinning and flip it upside down, it seems to be spinning in the opposite direction. The spinner has mass set a distance from the axis of rotation so it has angular momentum when spinning. Angular momentum is a vector which has a direction clockwise or anticlockwise. This will always be conserved unless a resultant torque acts. So angular momentum will be same when flipped upside down. It will be spinning in the same direction but viewed from the other way up it will look as though clockwise has become anticlockwise. It's just your viewpoint that has shifted.
