I bought this for cycling, but use it more for running. I have been doing a lot of cold weather running this year (as cold as 5 deg F) and this warmer has been excellent for my neck and face.
I cut a mouth opening since any limitation to air flow is a problem.
Works nice. Better than a balaclava when riding as you can strap up your helmet and then pull up the gaiter. This gives you more options to change position if getting too warm or cold. Should have gotten one years ago.
Prevents drafts and icy winds from going down your front. Pull it over your nose and mouth to warm up your respiratory system.
Also works well to retain some heat in downpours.
This is a great product when the temps dip below freezing. I've worn it in temps down to the low teens and nasty winds and the warmer does a really good job at keeping me protected. The fabric itself is fairly thin and doesn't seem like it would do a good job, but it really does. I typically just put it over my mouth and nose on descents and pull it down when I am climbing. The few times that I have left it on my face climbing it does seem to allow a decent amount of airflow out so my glasses didn't fog up. I've been using it for about three months now and love it. All around great product, no complaints.
I use this with a skull cap and it is long enough that I can pull it up in the rear and capture it under my helmet to securely hold it in place. It can easily be pulled up over my mouth & nose for extra warmth. Good stuff.