I had them in my old house & they were useless, depends if you have old ones or new ones? Apparently the new ones are better (but I wouldn’t know as mine were the old style). They used so much electric even on E7 and come the morning you’d be sweating and opening the Windows by lunch time you’d be freezing again and all the heat was gone.. there is vents that you close at night whilst they heat, then you open them when it’s cold to let the heat out (supposedly, mine just let it out straight away

).
I ended up changing my tariff to a normal one as E7 is cheaper at night, but a lot more in the day so doesn’t work out well unless you use almost all your elec at night and next to nothing in the day time. I got an electric fire for the living room and shut the door when I needed to use it, then had an oil plug in at the top of the stairs to put on for a couple hours before bed time. Worked OK for me but wasn’t great really.. sorry