I'm holding a FR clear Proton Axis, and a flat blue Neutron Axis in my hands. If you want to hyper-analyze the two, the bead seems less than a half a millimeter bigger on the FR. And the Neutron is a little flatter. That's it.
For all intents and purposes, they are the same disc. I haven't thrown this FR in a long while, so I can't comment on its flight, but both discs feel the same in my hand.