I've not been a fan of cycling jackets in general. They've either fit me like a deflated hot air balloon, have terrible packability, or are for the hardcore days (i.e. Rapha softshell or Hardshell). My first encounter with something that straddled the line between weight-to-warmth, waterproof-to-breathability, and had good fit and finish was Castelli's Gabba line. But even those pieces were too warm if the temperature rose a little, and packability, even on the vest was still relatively large. I live and ride primarily in the Bay Area so temps range from 40s to 60s in the mornings and in the winter, the temps can stay right around that 40-50 range. A ride can take you against the sun, but then into a back valley that drops 10 degrees. A jacket like this keeps all of those concerns away. Paired with the PowerWool thermal jersey, you're golden. Layer with a thicker base layer or wool, or even a regular LS wool baselayer or Henley that's not cycling specific, and this jacket is casual and high-performing enough to carry you through a wide range of temps. I love that it fits more like a jersey and has a lovely soft handfeel but is still a shell — they are not kidding about the stretch! You know how everyone loves a "shacket" these days? This is that for cycling.
On the first ride with the Magic Shell, I only took it off once when the sun was on for a full few miles, afterwards in the shade the thermal and breathability aspect as well as moisture repelling all came through.
I almost bought this jacket multiple times over the last two years, and truly regret it took me this long to get it. My first impression when the package first showed up, I was so surprised at how light the jacket was. We have had some super cold mornings in LA recently and the jacket has been perfect for the 30-40 degree temps. I have paired it with the Power Wool jersey and it has been the perfect combo for my rides. The Magic Shell's balance between blocking the wind and still being breathable is truly what makes it magic. Clothes always fit me funny because I have random measurements (5'7" 190lbs 34 inch waist and 42 chest), so I went with the Large. It fits me perfectly with exception to sleeve length. I kind of knew that would be the drawback to getting the large, but it fits perfect around the chest and waist as well as over the Power wool jersey.