I have worn them while riding my 2012 Suzuki GSX-R750, which has no hand guards or heated grips, in temperatures ranging from 70 degrees down to 40 F. I have worn them on my 2007 Suzuki V-Strom 650, which has hand guards but no heated grips, in temperatures from 55 degrees down to 40 F. The gloves are surprisingly warm, which is code for: it takes 45 minutes before my hands get cold instead of 15 minutes like most multi-season gloves.
They are somewhat stiff when operating controls but after putting a few dozen hours in them I can tell they are breaking in and loosening up a bit. They are comfortable, easy to put on and take off, and don't make my hands sweat (which is rare; I have sweaty hands). I've not tried to put the gauntlet under my jacket sleeves and I doubt it would work if I tried. These gloves are allegedly waterproof, but I've not yet ridden in anything other than occasional showers. Normally when it's raining hard, you want your jacket sleeve to fit over the glove. The gauntlet on these is big enough that it's not feasible to do so. If I were wearing these in anything more than moderate rain, I'd wear my Aerostich triple-digit rain covers over the top.
My ultimate test of a product's worthiness is value: does it's features and quality exceed the cost? In the case of the Cortech Scarab Winter Gloves, I definitely feel they do. They are a good value in an armored, gauntlet-style waterproof glove.
Update: 12/31/2012
I have since worn the Scarab's in colder temperatures, down to the upper 30's, riding both my V-Strom with hand guards and my Gixxer (no hand guards). The gloves work reasonably well and I maintain adequate dexterity. I have used them with a pair of silk glove liners and find my hands are comfortable quite a bit longer before they get cold. So far I would say these gloves exceed my expectations.
