Love everything about it except it's a little snug especially around arm holes near the chest. To be fair I am not a typical fit since I'm 70"/205. I am a former college football player that still lifts weights regularly. Other than that, I took the vest out on one 4 hr ride in the Tetons with weather in the high 50s and wore it all day and it performed great.
My first purchase from Ornot and definitely not the last! The customer support is stellar, the little shop in SF is beautiful and most importantly, the vest is awesome. Their design is just perfect from the aesthetics as well as functional level and the vest keeps me warm crossing bridges and sprinting down the Hawk Hill. For folks wearing Medium, I recommend sizing up to Large (or even XL) to be comfortable.
Been cycling for a year and dropped so much weight, went from a large to a medium. I looked at every other nice brand out there to see what was up, circled back to Ornot. Like every other piece of Ornot kit I own, performs so well, looks so good, and the quality is premium and top notch.