In reply to John R:
I own both but use the photon x far more. The difference for me is that the photon is packable in a sensible sized stuff sac for carrying on my harness and the citadel is not. I don’t like climbing with a pack.
The citadel is of course warmer but the photon has been fine for my season of ice climbing in Norway, Canada and the alps. I do run warm though.
The only gripe i have with the photon is that rab seem to have changed the cut on their jackets at some point recently such that they are tighter around the chest than they used to be.