A lot of people (not those here, naturally!) seem to think that winter tyre performance is a subjective thing.
It is not. Categorically not.
When the temperatures are at an average of 7 degrees C or below then winter tyres perform better in pretty much every measurement: accelerating, braking, turning, hill starts, descents, ascents etc etc etc.
That is all irrespective of weather conditions. Throw in snow, ice, rain and the winter tyres defecate from a great height on any summer or all season tyre.
In most peoples opinion, mine included, and given avg temps of 7 or below I would consider the heirarchy of mobility (I should trademark that!) would be:
4x4 on winter tyres
FWD on winter tyres
4x4 on all season tyres
RWD on winter tyres
FWD on all season tyres
RWD on all season tyres
4x4 on summer tyres
FWD on summer tyres
RWD on summer tyres
As for are they appropriate in the UK, that really depends on where you live and what car you drive day to day.
I live in the Yorkshire Dales. We get proper weather. Most winters we'll have snow on the ground for 20+ days, icy conditions almost daily from Dec-Feb, lots of rain and standing water.
Here is a clip of me testing out my new winter tyres on the 944 this March. This was only 4 months ago! -15C, heavy winds driving the snow across the roads. The clip is me leaving my house and driving the one mile of country lane to the nearest gritted(ish!) road.
It is a horrible road in winter. Adverse camber, a nasty steep 90 degree turn and, going away from my house, a steep descent.
I was pretty pleased with the performance of the Yokohamas.
944 winter tyre test on Youtube