The Ultra Clava is pretty awesome.  I have a pretty big head, so I bought the L/XL version.  It does fit a little tight, but I can get it on without any major issues.  I think it being so tight-fitting would benefit those who want to use the mask under a helmet.

The mask is warm and lightweight.  You can wear it as a hood, mask, or clava (covers everything except your eyes.  The nose-cover is something I especially like.  I would have given it 5-stars, but as I said, its a bit tight and doesn't stretch all that much.  Don't be so worried though... I have a big head and it still fit.