I couldn't find a decent review of this jacket on the web, so I here you go. I'm 5'10, 145lbs and I end up in medium Pearl Izumi jacket. The chest is still slightly baggy, but the arms and torso were too short on the next size down. For reference, I usually wear a small or Euro XS jersey.
The 3x1 is basically a wind-proof insulated jacket inside a non-insulated, wind-proof, very water-resistant soft shell jacket. They are held together via a button snap on the sleeves and collar, it works well and is simple. Once the jacket is on, it feels like a one-piece jacket.
Wearing only a short-sleeve baselayer, this jacket excels from 35-45 degrees. Any colder and I need an additional layer. At 45+ the inner-insulation layer needs to be taken out or it gets too hot. The outer layer is good up to about 60 degrees, any warmer and it makes more sense to wear arm-warmers and a vest.
Both layers breathe extremely well in all temperatures. However, your only options for additional venting are the front zippers. But, there is a clever snap on the outer-jacket collar that allows you to unzip without the rest of the jacket flapping in the wind. The zippers are very high-quality, and easily operated with gloves.
The detachable balaclava is a nice extra. However the internal stow pocket is located under the collar, inside the jacket, at the crook of your neck. It's isn't big enough for the balaclava and it feels like you are riding with a tennis ball behind your neck if you cram the balaclava back there. So in the end, I treat it like a regular balaclava and stash it in a jersey pocket when I don't need it.
The left breast pocket on the outer jacket has a headphone port. The right breast pocket and the single breast pocket on the inner jacket do not. The outer jacket rear pocket is huge and stretchy, however it is still not big enough to stow the inner jacket if you get too hot. You are stuck with the insulation layer if you choose to use it. The insulation layer does not have a rear pocket.
Overall the jacket looks great, the soft shell material has a great hand to it. You could also wear the insulation layer by itself, but it's lack of pockets make it somewhat useless in that regard. They are both styled enough to wear off-the-bike.
My only complaints are wishing it fit a little more "euro" snug around the chest, the useless balaclava pocket and the inability to stow the insulation layer. It's nice to now have a jacket that I can throw on without stressing about extra layers and just ride out the door.