Catalytic heaters, candles, or other heat sources inside a closed space such as a car bring dangers. They also bring heat. If someone is trapped in their car in winter a heat boost of 20 degrees is very helpful. If they don't handle it correctly they die of CO poisoning, burn up, or get serious burns. If they don't use it they die of hypothermia. Dead is dead. OTOH, if something like this or a can or sterno or a NuWick candle is used correctly it may stave off hypothermia for a time which may be sufficient to allow them to be rescued. As with all tools the hazard is not the tool but the fool.