from what ive read, they are better than snow chains and winter tyres...also thy seem to be cheaper than snow chains. also dont have the problem of swapping out your wheels for snow tyres, or the extra outlay for winter tyres when its only bad for 1-2months out of a year here...
I don't see the extra outlay for winter tyres any issue. Sure you only use them for a few months but than you store them till next year and the year after...
It also means your summer tyres will last longer as they are not in use.
It's been snowing here in the Netherlands for over 3 weeks and I wouldn't drive without winter tyres. Also if I cross the border into Germany I must have them by law.
I haven't used Auto socks or chains but anything option other than just summer tyres has to be a good thing. It will save you having a silly accident going at 20 or 30km/h just because you can't stop.