> It's not exactly a vector...

That's right. It's not a vector because it doesn't "transform" like a vector.

If you take a vector and rotate about an axis by 360 degrees, you get the same vector.

If you take a spinor and rotate it by 360 degrees you get a spinor which is "flipped". You have to rotate the spinor by 720 degrees to get back to the same spinor.

This is intrinsically weird, but that's QM.

It only has direction + magnitude right? (±h/4π)e_i for some unit vector e_i.

So it can be written as a vector? No?