Good device helps to warm up the hand and avoid severe frostbite. It is not for a short outing in the cold, it is intended for situations where you need to keep your hands in the cold for hours, like in the army. It requires special charcoal inserts, which are provided separately by the company. The only downside is that you need to figure out exactly how to light the charcoal inserts, as it requires a specific technique, otherwise they go out and you have to light them again