Wish I had the Flash Down years ago, I live at 8000 ft in the Colorado mountains and this is a great piece of gear. I own the Ultralite sleeping bag and Meltdown jacket the quality is excellent with Western Mountaineering.

You don't even know it's in your pack because it's so light...great for touring, backpacking, wearing around town, climbing etc. When I take it out I usually wear a hardshell over it. Super durable because it was made in San Jose and not in China by 30 seamstresses. Do yourself a favor and buy something that will last a lifetime. WM for the win everytime.

I got this layer with the knowledge that it would make all my other layers obsolete. I live in Denver and love the 14er summits. I wanted something that I could wear to a wedding and could also buy me 45 minutes on a 14er summit. Having fun outside does not have to be ruined with bad clothing choices. Sometimes you need to travel to Patagonia to get a puffy jacket recommendation.

I've used the flash jacket around town in mid 30 degree (f) weather for a couple weeks and took it on a 16 mile hike in the Ouachita Mountains after Christmas. Temperatures were in the 40's (f) during the day and too warm for anything more than a base layer, fleece and shell. However at night the temps dropped into the 20's and teens by early morning. This puffer was the perfect solution for these cold temps. A perfect part of a 4 part system. Base, fleece, puffer, shell. I originally thought I wanted a puffer with no hood, but on my recent trip I really appreciated the hood and wouldn't even consider ordering a puffer for trail use without one.

This is a great jacket and a great company but for me it had an issue that couldn't be overcome. I used it a few times this hunting season to stay warm when not moving and found it to be exceptionally warm for the weight - I barely knew it was in my pack.

I returned this however because the light-weight shell fabric used has a propensity to bleed more feathers than I've ever seen before Its up to you, but personally I want my jacket to be a bit more durable than that.

I still like the company a lot and traded up to their XR Flash series which is heavier but more feather-proof. Am very happy with the upgraded version.

So sorry that I've not addressed your questions for such a long time. Let me attempt to do that now as objectively as I can.
The Rab Microlite Alpine is a vastly different animal. It has a W/B outer shell and weighs in at 21 oz. vs. 9 oz. here. The Flash sweater is intended as an outer layer for moderate days and should undoubtedly be layered under a W/B shell when skiing trees or when the wind is howling. Yes, the lightweight fabric will snag on tree branches when cruising by in the steeps. The combination of 850 minimum fill power down and lightweight, completely breathable fabric causes it's comfort range to be extremely versitile. From 65 degrees F to 20 F, I typically feel like I'm at room temp while wearing my Flash. Adding a waterproof/breathable layer to the outer fabric increases its durability (still risky in the trees) and it makes it warmer but will also narrow it's comfort range. Warmer temps will more readily cause overheating. I have both the Flash XR and the regular Flash. Probably if I lived in the Pacific NW, I'd wear my XR more. Here in Colorado, I don't even carry fleece in the backcountry anymore. This jacket with a lightweight Gore layer on top and 1-2 thin wool layers underneath is the most I've ever needed on our coldest -10 degree days. Hailing from Minnesota, these Colorado temps are admittedly pretty moderate.
For the record, the Flash XR is plenty water resistant for any wet weather I've encountered short of a downpour.
I've uploaded a photo of my Flash after 3 years of use. If I'd skied trees with it unprotected, it would have patches all over it. Having said that, I've not babied it either. It is either in my pack or thrown in the back of my car or stuffed into the tankbag of my motorbike whenever the temps are anticipated below 40.
Regarding its durability, as Yvon Chouinard so aptly put it: (paraphrasing) Having the best gear is no replacement for knowing how to use it.
Use this jacket wisely (not over-protectively!) and it will last a very, very long time. It will also become your most used jacket as it has become mine.

This is an incredible jacket! I can actually ski in it and not over-heat as I usually do with other higher loft jackets. The shell of the jacket repels snow well. There is a tradeoff for the extremely light-weight material: It rips easily, so you have to be very careful skiing by trees or bushes. I have patched a few areas because I am not careful. I now wear a light shell to protect the jacket when I am skiing in the trees. Recently I purchased the XR version of the Flash jacket. It has a more waterproof shell, an adjustable hood and zipers on the pockets. For wet snow weather, I will probably use the XR model. The Flash jacket is the warmest jacket for its weight. Westernn Mountaineering uses high quality down and produces high quality products. All their products, including this jacket, are worth the price.

You need to know right off the bat that I'm the sales rep in the Rockies for Western Mountaineering. I'm unabashed about extolling the virtues of Western down bags, jackets, pants and booties.
I've owned many down sweaters in the course of my work in this business. This is the best I've ever used. It's lighter, more compact, warmer and more comfortable than any other. Here is my experience: The jacket with stuff sack weighs 9oz. on my postal scale. The fit is generous with a very comfortable hood design. Don't look for fashion here. You won't find it. Instead, decide if you're looking for the lightest, most compressible, warmest down sweater on the market. If it is, you'll keep it in your pack at all times like I do, waiting for the next opportunity to put it to the test. You'll love it too!