Thanks, yeah think I've read about that version before. But "the magnetic field spins the electron around once", doesn't this feel a bit weak? You could conceivably just define "spin around once" as the B-field manipulation that returns the amplitude to +1, not -1. How do you define the B-field interaction in a way that is comparable to "spinning something around once"? I'm not trying to be annoying :) I feel this really is at the core of the spin-1/2 "rotate twice to rotate completely" confusion..

Because it's the "rotation" in comparison to the surroundings that cause the change in amplitude, a global rotation of the electron particle and the rest of the universe doesn't cause the electron to change amplitude, as then it's just a global coordinate transformation.