I haven't seen these before. I don't think it matters which way the spring is installed.
That said, I would install such that the tighter coil side (firmer side of spring) is closest to the barrel peanut. This is the side of the spring that will move less. Since the barrel is not moving and the slide is moving you would want to put the spring to match the movement.
Let us know how it performs and if you feel any difference in recoil.
Cheers,
Toby