John L.wrote a review of Castelli Alpha ROS Jacket- Limited Edition - Men's on January 11, 2018
Familiarity: I've used it several times
I've been very pleased with this purchase, primarily because the product works as advertised. I have a few other cold weather jackets, but nothing that works as well as this one in providing good warmth, moisture management, wind and water resistance, and good fit with other parts of your kit.
Warmth: have ridden into the low 20's in Northern Virginia weather with a long-sleeve baselayer underneath and stayed plenty warm. The usual problem areas on most jackets are the arms, they start out warm but get cold as you start sweating underneath -- not so with the Alpha.
Moisture management - This is why your arms don't get cold. The multiple high performance materials around the arm let moisture escape.
Wind and Water Resistance - The dual-layer concept allows you to control the balance of airflow on your torso much better than traditional vent zips by ensuring that you still have some breathable insulation in the direct wind path. That pulls away excess heat and moisture over a wide range of needs -- fully zipped at very low temps, and much more open as you start working harder or the temperature climbs. Water resistance is similar to a Perfetto/Gabba jersey. It will hold off a mist throughout your ride, but don't expect it to keep you dry in a steady rain for more than about an hour and change.
Fit - The fit is typical for Castelli (i.e., runs small), I wear a medium in most race-fit jerseys (6'2"/168lbs), and a large fits me snug, but with room for baselayers underneath. Unlike some other jackets, the sleeves are snug enough to stay put underneath multiple types of winter gloves (fully insulated or thinner wind-proof style), yet don't feel constricting. The extra material on the back of the neck is a nice addition to a spot that frequently gets cold, but doesn't get in the way of a neck gaiter or balaclava.
In short, at a price much lower than a trainer, this jersey will let you ride in a much wider range of conditions than you thought you could.