If a curb's shanks are swept back like that, it gives the horse a little warning as you pick up your reins and alert them that you are about to give pressure or a cue, etc. Does that make sense? When the shank is straight, they don't feel anything until the rider applies pressure. So, in a way, it is more mild, if that makes sense.
I don't really have much of an opinion on this. We don't have mounted police here and I don't know much about pelhams and why they are apparently frowned upon. I do love that heart breastcollar on the horse on the right though.