Bryan,
I got my Mountain Star in the mail yesterday and at first glance I agree 100% with your comments. It would be right to describe this as just about halfway between a conventional "hard" windshirt [Houdini, Wraith, Cirrus, etc.] and a super-breathable "soft shell" windshirt [Boreas, Chocklite, etc.]. The weight range corroborates this story — the former group is around 3oz – 5oz, and the latter group is maybe 9oz – 11oz. The Mountain Star falls right in the middle at ~7oz. I haven't thrown my particular one on the scale yet but will update when I do.
Also agreed that the hand, feel, and drape of the fabric is exceptional. This is a purely aesthetic concern but it certainly doesn't hurt — the fabric feels great, smooth, soft, quiet. The colors are great, the notions are straightforward, workmanship appears on the high end. Altogether it makes a great first impression.
The fit is not impressive, but not bad. I find it a little boxy. This seems to match with the older Lite-Speed jacket that I just sold on the gear swap. I usually feel just right or a little roomy in a "regular" USA medium, or perhaps a touch snug in a "trim fit" USA medium. E.g. the Boreas is just right for me. But, based on experience with Montane, I ordered a UK large here, and as expected it fits me more like a "roomy" medium which allows (or encourages) layering, but is not so large that I look like an 8-yr-old boy when wearing it. The coverage is decent, definitely a few inches past my belt which is desirable for me. Sleeves are way too long for me, but that is typical as I'm a small guy — I had the same problem with the Boreas and with most size medium *anything* that I wear.
Since the fit is something that I might call halfway between a USA medium/large, and the fabric has some slight stretch to it, this piece might fill an important niche in my quiver. It could be the windshirt that is both A) just trim enough to work as a main action windshirt during the daytime over a base layer or light fleece, and B) also just roomy enough to throw on over a nighttime puffy layer, to even out cold spots and provide some extra precip protection, without compressing down / synth loft. We'll see. Of course YMMV because this last comment is a purely individualistic consideration.
I did the old mouth-breather test on the fabric and again it seems to fall midway on the "hard" and "soft" windshirt continuum. Air flows easily but requires a bit more respiratory effort than with my Boreas. Perhaps conversely, the DWR will be a little better. Your test (Bryan) seems to suggest as much.
I'm considering the Lightbeam shortly and will probably stare at these and don / doff them about 20 more times before I actually feel confident enough about taking one out for a run, bike ride, or test hike.
But overall the Mountain Star looks promising.