I had a fiesta a few years back, I bought it from my mate who works at a garage/tyre place, and he'd just put a set of winter tyres on it.
The tyres were fabulous for short journeys in the snow/ice but once the ambient temperature rose either in the tyre, or one of those lovely sunny days you often get in winter, they would flop around all over the place and make cornering/braking very interesting! I soon bought some secondhand alloys and tyres from ebay and sold the winter tyres on.
If I lived somewhere where they had proper winters, I wouldn't hesitate in having a set (as long as I had space to store them) but wouldn't bother again in the more temperate East Midlands.
