They do work well but are not for anything more than temporary low speed use, so best to consider them as a more user friendly alternative to snow chains.
As an "alternative to winter tyres" not really unless you also hold the view that having a set of snow chains is also an viable alternative to winter tyres. It is not, both are really just short term fixes but then maybe that is all most people need.
To put it in context, when I drive to Austria in winter always have winter tyres fitted but also carry chains. But in recent years I have never had to use them despite encountering really vile autobahn conditions (chains and snowsocks useless there) and very treacherous mountain roads.
In this country though snowsocks have a lot to offer for those without winter tyres , just do not expect too much. As it says on their website:
"The bottom line is that AutoSock will provide a massive boost in all round confidence when driving on ice and snow, and hopefully "Get you home" or to wherever you're going, but don't overcook it, i.e. you should always drive with particular care in wintry conditions."
