There are a few pieces of gear that embody near-absolute perfection of design, and the Black Diamond Couloir harness is one of them. What do you want in a mountaineering harness, assuming of course that it's reliably safe to begin with?
First and second would be light weight and low profile, since you'll be wearing it every day and moving across technical terrain in a variety of conditions. The Couloir has you covered, with wide, flat webbing that provides support while hanging and fits underneath a pack hip belt with a minimum of fuss. Third would be adjustable quick release leg loops, for correct sizing and donning/doffing the harness over crampons, skis and monster big-mountain boots. Check.
After that it's all gravy: two lie-flat gear loops, four ice clipper slots, offset buckle, haul and belay loops, and a reasonable price. All check. Oh, and one more thing: it only weighs freaking eight ounces! There are lighter harnesses out there - we've used most of them, and for race day or single day outings on vertical ice or rock we'll grab a specialty harness - but we only have eyes for the Couloir when it comes to expedition use. It really is that good. This holiday season do the mountaineer in your life a favor. If they don't have a Couloir in their closet, hook them up.