I wasn't sure this would be worth the premium price, but when I rode to work this morning and it was -11 and windy I was very glad I'd made the investment. Comfortable, fits under my helmet, ski goggles (Oakley A-Frame, I believe) and a hood or two or three. Tuck the bottom under your jacket(s)'s collar and you're sealed tight against heat loss and wind. The mouth holes and nose opening make it easy to breath through, though by the end of my ride I was feeling a little claustrophobic.
This was probably the coldest air I've ever ridden in, and I'm from Minnesota, but I didn't even feel cold because of how I was suited up and this Seirus Ultra Clava deserves a lot of the credit for that.
One note: I ordered the Large/XL, and it's still snug. My head is big but not enormous, so if you're not sure which to order lean towards the XL.
I bought this balaclava for my husband. He said the fit is perfect, the material is superior, and it is the most comfortable one he has ever tried. Other balaclavas have either been too loose or too tight around his nose. And, of course, it protects from the cold very well.