I obviously know nothing about the Swiss product, but winter hikers in the cold parts of North America use similar products, marketed as "hand warmers" or "foot warmers". They come with a warning not to use against bare skin; the foot warmers go between boot and sock, the hand warmers between glove or mitten and the thin liner gloves most of us wear under the main glove or mitten.

With temperatures often around 0F (-17C) or lower, they are a Godsend. I buy them by the box of 50 (pairs!).