I live in area that is typical in the low 40s in the winter and 50s in the spring. The base layer keeps me very comfortable when paired with cycling jacket in winter and long sleeve jersey in spring. Fabric is soft and dries quickly. I have one that has held up well for over a year (wash in delicate cycle, then air dry overnight). Sizing is accurate and fits snug while allowing good freedom of movement. I would recommend this base layer over Castelli Flanders product which was too loose fitting.
My hands don't tolerate cold well (Raynaud's). So I have to use lobsters with a liner in anything below 45 degrees. These cover me pretty well from 50 to 55, 45 to 50 with a very thin liner. They get a bit moist inside if it's too warm.
One issue is the length of the fingers. I have another pair of Castelli full-finger gloves (XXL) that fit, well, like a glove on my size 8 to 8.5 mitts. The Perfetto is an XL and extends off my fingertips between 5 and 10mm. The silicone grips are nice. Haven't tried them in the rain yet - but work well in a mist/fog situation.
When these came I was skeptical. For what these black diapers cost they looked flimsy and the they just feel awkward off the bike. I normally wear a small in bibs and the small fit a bit tighter than Assos and about the same as Giordana FR-C bibs. The Chamois feels like it is an awkward place but it works better because you don't end up riding on the chamois edge. First ride I didn't really notice them and second ride on them did a 100 mile gravel race in wet weather and they did great. No raw spots even though lots of short punching climbs that have you moving around. Best compliment I can give them is I really just forgot about them during the 6 hr day. Now we'll see how they hold up.
I mean, it doesn't actually cover your shoulders, but it does work great for transitioning from winter into spring. Fit is a little relaxed for road, but it is nice to have it not be super confining for mtb duty too, and it's burly enough to not feel too precious for dirt duty. It also doesn't flap or make noise when descending, so the fit appears to work fine.
It vents really well, while maintaining core warmth. I've worn it on a few longer rides that start out in the upper forties and get into the lower sixties and it's not stifling like a regular three layer jacket would be. Rear pockets are nice and structured enough to be useful, unlike some ultra light gear where they're mostly just the idea of pockets.