I'm thinking of trying one of these. I have a fleece neck cover and a neoprene balaclava. The neck cover is nice, but not quite enough cover for real cold riding. The balaclava makes my helmet a bit tight on the top, and it tends to fog the shield more. This might work better with the nose holes. The price is cheap enough it's worth a try.
I have one that I used when it got cold outside (i.e. -30 or below) and I was out skiing or something, but never tried it on the motorcycle. I have a full-face helmet, so no real need for it - I do have a very warm neck-warmer thing I got from some online motorcycle shop that you pull around your neck before you put your helmet on, and makes a HUGE difference when it starts getting cool out.
Yes, as a matter of fact, I own the clown mask. It works, but is not for a closed-face helmet if you wear any type of glasses. They fog up as soon as I breathe once I fasten my mask. Same for any face shield that isn't fog-resistant. At least that's been by experience with it. It's great with a shorty helmet, helmetless, or with my flip-front with the front open.
One thing that I DO use in cool or cold weather is a Buff. http://www.planetbuff.com It has some of the same problems that the mask has, but it's advantage is that it can be worn in so many ways that you can almost always find a way that the buff will work for you. The buff is all I use even when riding my Ninja in 40 degreee weather between my riding jacket and my helmet. It works for me! :action:
We have two sorts, one similar to the one pictured that is baically a tube that can be worn either just around the neck or brought up over the face, but also another wooley sort that had a flap that hangs down at the front and back helping to seal out draughts and keep chest and back warm. It is very verstile and can be worn in various ways from a head warmer sort of hat to a scalf with head cover.