I used to have them when I lived in Seacroft - in a Council flat. Very expensive to run. I just had the one (of two) running in the living room. I made the mistake of turning them all on. The meter needed water cooling, it was spinning that fast
I was on a token meter at the time. I think it used about 50p a night. Also had 6KW immersion heater - also pricey. Anyway, back to the heaters. They would charge overnight - they were all on a seperate circuit, that had a timer (controlled by the electricity supplier). Between midnight and one they would start charging (and emitting heat) and would stop about seven-to-eight in the morning. During this time, the electricity would switch to a cheaper tariff. Economy7 I think it was called. I could control how long the heater charged for, but I always had it set to maximum - for reasons I'm getting on to. Now, during the day, even with the heating turn down (basically a flap control, like Bop says), the heater would be HOT - I accidently burnt stripes into my wrist with it. Just caught it a glancing blow when hanging out the washing. Sizzle
Trouble is, the heat would run out around ten on a night, and by eleven it would be heatless. Many a winter I sat watching TV with a hot-water bottle on my feet, wrapped in a blanket. I had a fan heater but it cost too much to run, and due to the size of the room, the heat didn't last once the heater was turned off. Terrible times.