Little short of brilliant. I've had them on hire cars in Sweden and Finland, with and without studs, and the difference is night and day.
Most UK road car tyres have two problems - too wide (so they don't cut through the snow and slush, and spread the load too widely on ice) and too hard (temperature rating A basically switches off below 45 deg F, so you get nothing from the compound) to run on snow and ice in the UK.
Winter tyres are softer, thinner and with a block tread designed to do two things - shed snow/slush and switch on a much lower temperatures. The concern is that on clean tarmac in a usual winter temperatures, they will wear faster, and the handling will be below what you get on the usual tyre. If you can live with that , then they are worth an investment.
My experience in the Nordics is that on any cold surface, snow/ice or not, they give more grip in every situation, and allow you more margin for error. However, I haven't had problems in the UK with summer tyres over the winters. The main reason for getting stuck is sheer volume of snow, or other idiots abandoning cars in stupid places just because they can't drive properly. If there's lots of snow the car just can't ride over, winter tyres won't help, and if there's a risk of idiots on the road I just stay home. HTH
