The Bottom Line: A hyper-specific piece that is great for those who have trouble finding sufficiently breathable hardshells for winter.
Back in 2013, Black Diamond released the Dawn Patrol Hybrid. The front and shoulders were a waterproof material, while the material under the arms and on the back was a light softshell. The jacket was too heavy, burdened by a total of five poorly distributed pockets. At the time I wished Arc'teryx would make this jacket. And they did a couple of years later.
The Procline had all the improvements and features I love from Arc'teryx, chief among them the coverage of waterproof material that extended over the shoulder down as far as the shoulder blades. The second was the Napolean style breast pockets. While wholly unpractical for day to day use, huge pockets that sit too high are great when you always have a pack on. I can actually cram skins into each pocket, maps fit great, and they are awesome for keeping spare gloves on hand. Lastly, they added my favorite feature, HemLock: This prevents the jacket from riding up under a harness or waist belt. I've actually added these to some of my other jackets because they work so well.
So how does the jacket work in real life? In the dry Rockies it was pretty good for atrocious winds or slightly rainy days. While it had about the same breathability as my Gamma MX, it lacked the versatility. In the Coast Range I was hoping it would be ideal for rain or wet snow, but you do get drips running down your back when the snow melts or the rains are heavy enough. I quickly ended up opting for a hardshell if I thought there was a risk of wet weather.
I do like the Procline. It has a use on a certain type of trip and on drier days when you need front weather protection. I'd often put it on at transitions over my softshells for a sweet and quick downhill transitions. It certainly could be worn as a top layer for skiing, though I found my Epsilon or or my Psiphon to more ideal once I warmed up.
The best use for this jacket I found was cycle commuting with a pack. The breathability and forward-facing waterproofing was ideal. And my sweaty back was protected from the drip by being hunched over. Honestly, it you are a daily commuter who doesn't use panniers, this is definitely the best way to get around in rainy winters.