First: The Füßwärmer is easy to use. Simply pick from the box, put the plug into the socket, the controller to the level 1, 2 or 3. At Level 3, the foot warmer is me still too weak. Degrees in winter you want warm feet, as this is also the risk of becoming ill, is less. Comfortable the foot warmer is only for a time: You have to sit on, so you can feel the effect. If I want to lie down, I need an extension cord ...
Conclusion: A luxury item, which you probably do not need it. A conventional hot water bottle does here also, this is also much warmer - and you can lie down! No Best Buy.