The pictures online make it hard to tell about the build of this jacket. There is no storm flap and the powershield O2 seems pretty weak, this is very much a layering piece, and not that warm without a shell to go on top. Go look at this in a store before you buy it. I found the seams and other minor quality details a bit sub-par for the Arc'teryx price. Doesn't seem to make a lot of sense to me to buy this jacket, go get a windproof fleece which is really all this is. The Hyllus is only really great for mild to cool weather or being highly active in cold temps with low wind. For a super warm winter softshell for bumming around town and belay-bitching in the frigid mornings try the Firee, that jacket is bomber. If you want a sick alpine softshell that's not gonna sweat out look at the Venta instead of the Hyllus. No room for the Hyllus on my coat rack - there are better options out there.
Picked this up from REI scratch and dent $50. I prefer it over the Arc'teryx Miura for the better organizational setup. I just took it out for a day packed w/ 60m rope, single-pitch trad and sport racks. + shoes, chalk, harness, lunch, 3 1L nalgenes, hydration bladder (in special pocket), personal effects (in special pocket) - sunglasses, wallet, keys, etc. Found that everything was EASY to access without dumping the contents of the pack. Also everything except helmet fit inside no problem. Plenty of room for everything you need for a day at the crag.
I found that the pack is a little short for my torso (I'm 5'11") - hip belt sits too high, so had to share some of the load on my shoulders. Even so, a 5 mile trek fully loaded was still a comfortable enough carry.
The beefy construction and many pockets adds some extra weight to this beast. I would not use as a substitute for regular backpack due to the boxy shape, lack of waterproof zippers, no top compartment. Strictly for climbing use. Also probably not great for peak assaults or mountaineering , etc. Included rope tarp is ok but rope management is easier to just throw in the 'ole rope bag if going to be moving from route to route.
The good: Got this for my main belay to fit with smaller hole on GriGri. Instantly attractive, lightweight, feels great. Locking mechanism smooth like butter and never jams even after catching a hard fall. Really nice design.
The bad: Slippery little sucker sometimes likes to move around into cross-loaded position
The ugly: Screwgate is so smooth acting that simply a brushing motion of taking up rope for belay can unscrew it if you aren't careful! Have looked down numerous times to see my biner has become totally unlocked - not cool!
Solution: its great if you always remember to keep the gate on the opposite side of your belay hand.
Used these for early season ascent of Mont Blanc with smart wool mountaineering socks. Super comfortable for the approach and the summit. Toes got a little cold climbing the dome but were fine as soon as the sun came up. Half the guides in our expedition wore these. Totally burly, handled crampons really well. Stayed dry after three days of continuous snow slogging. If going to higher altitudes or colder temps (ie Rainier) would get a supergater.