I hear ya 🫂. I believe this to be a false claim on their part.
750-1500 watts mean joules per second. Now their device might reduce hear output of the heater by 30% by reducing current by 30% let’s say, but they aren’t changing the heat gotten per kWh, which is what people think when they hear that the electricity used went down by 30%. It would be the Nobelest prize of all Nobels if they could do it.