They are, it's well documented. They have a softer compound so are grippier at lower temperatures. You only have to put a summer tyre against a winter to see the difference.
I have been running winters for the last 5 years and they are far superior to summer tyres in wet and icy conditions. Above 10 degrees though they aren't the nicest of things to drive on.
So, been looking about and that. I'm not fussed about alloys given it's only 4 months or so a year. My question is if I bought some 17" steels, would I be OK putting these tyres on 205/50/17 or would they be too slim?