These work very well, no more numb toes even in very cold weather. Only lost a star as unfortunately one of the batteries disappeared whilst skiing. They clip onto the top Velcro strap of your ski boot so ensure they are properly secured before going.
I have suffered from Raynaud syndrome in my feet for a number of years which has made skiing almost impossible due to the fact that I have to stop every few runs to remove my boots and re-warm my feet to restore circulation. These warmers have stopped this!
I have just returned from a ski holiday where I was able to ski non stop for 3h up until lunchtime without any need to remove my boots to warm my feet. Now I wouldn't say that my feet felt hot but they certainly didn't feel cold as they normally would.
Relatively simple to install (I followed a you tube tutorial), the battery pack easily lasted all day and enabled me to enjoy skiing properly for the first time in years.
What a super early Christmas present, I could not recommend highly enough.