Just wanted to warn about the sizing of this product. Whilst they're rated as being suitable for a UK size of 8 - 12, I could only just get them to fit my size 10 walking boots. It's possible that they'd fit a slightly larger size shoe but not a larger boot, in my opinion.
Anyone with arthritic hands or difficulty gripping would struggle a lot with the fitting of these - irrespective what size they get, as the rubber is hard, tough and not all stretchy, even after several uses. My mother tried to fit the same ones (8 - 12) to her walking boots (ladies size 7) and found it very difficult to do, with a lot of awkward pulling and adjusting.
On the plus side, they're a doddle to remove (just grab the flap above the heel and pull down) - a complete contrast to putting them on.
I'm planning to leave them on a pair of boots (I'm fortunate in having 2 pairs) for icy walks and not try and put them on/take them off - other makes are definitely better in this regard (Get a Grip & Springyard for example).
Finally, unlike many of the other products available, the "spikes" are not sharp at all, as they're basically screw-heads. These are thus less likely to snap off but cannot be quite as effective as sharp points. Having said that, they seemed sufficiently gripping on the solid-ice pavements we're experiencing at the moment.
Hope this helps.