On Grim News: Harbinger can get Stance of the Ether Gate at level 5, almost the same thing as Omenwalk - doesn't let you teleport through doors (which you could do at level 5 with Ghostwalk anyway), but doesn't provoke for disengaging with it. IIRC Harbinger can't get flight from its disciplines, unless he takes Black Seraph tradition. Therefore, it would make sense to take Dark Wings first.