Everyone will need to decide for themselves if it is worth $500, but my first X did not have it, and my second one does.
Air is definitely fresher smelling, do not get as much dust on the dash or screen. Smells reduced, and to me the biggest benefit is no longer needing to smell obnoxious diesel odors when behind a truck/bus.
It is a welcome change, and much better than what Mercedes offers. They have a perfume dispenser, mainly for the Middle East market. Does not clean the air, but covers up body odors from inside.