When the Gan 251 M was first released their only released the Leap version which I would have thought would be the last to be released, it has a much more complicated mechanism with the new Large angle magnetic alignment system but that was released first. I am pleased to now be able to try the other two versions, they don't have as many features but are both still excellent 2x2x2s
Air: Just traditional magnets making it much lighter, interchangeable GES nuts.
Pro: Adjustable magnets, interchangeable GES nuts, corner/core magnet system.
Leap: Adjustable magnets, interchangeable GES nuts, corner/core magnet system, and large angle magnetic alignment technology which features much larger magnets in the core to allow it to snap in place.