Words cannot describe how good it feels to wrap yourself into one of these when you’re cold.
I heat my house with just a heatpump but it can’t quite keep up when it gets well below 10 degrees celcius and I’m too cheap to turn on electric radiators. I bought an electric blanket for 22 euros and I just heat that instead. Even just sitting on it makes a huge difference.
I keep my heat set to 60f/15.55c and use heated mattress pads on my bed and couch to make it tolerable. It has been between -7f/-21.7c and 24f/-4.4c this week, and it gets colder, usually mid January.
The cost to increase my heat from those temps to a somewhat more comfortable temp is literally hundreds of us dollars per month in gas (in addition to just getting to those temps from the outside temp), where the heated pads running 24/7 increase my electric bill by only a dollar or two a month (hydroelectric in my case, so hands down better, price difference aside).
The difference in operating costs is insane between heating an airspace and heating a body.
Heated blankets are a bit of a different thing; iirc they get warmer because they are meant to be above you, but could work the same way with that properly taken into consideration. You don’t get the sudden warm most of the time when using them under you, but it does help keep your core temp up. So lovely!
I’ve done this same thing for years and I love it! I splurged a few years ago and got a sunbeam mattress pad that has wifi so I can turn it on before I get into bed.