It's widely accepted that ebikes are some of the most energy efficient personal transport possible, because they're moving so little vehicle mass relative to passenger payload. Just 250 watts can give you rapid enough point to point mobility for trips up to 10 miles or so.
In the same way, heating and insulating people is vastly more efficient than heating air and brick walls. 100w of active electric heating together with a couple of layers of clothing is plenty to keep most people pretty comfortable at an ambient temperature of 14-15c.
I'll try using one as a wrist rest. In a cold room I can dress warm, but can't type with gloves on. The Jayne Mansfield hot water bottle would warm me up in more ways than one!
https://solar.lowtechmagazine.com/2022/01/the-revenge-of-the...
tl;dr is that heating people rather than spaces is a great idea with much more mileage than we give it credit for.