That comment got me curious so I went searching, looks like one supplier is called QETTLE and they have many videos on YouTube. And a FAQ that mentions energy use:
https://www.qettle.com/support/faqs , although the prices are probably from before the 2022 UK Government Omnishambles.
Here's another brand's innards of the reservoir: https://youtu.be/Q7TV73Y5kmo?t=614 . If I had to guess they keep it under high pressure so the water can be hotter than 100 deg C but still remain liquid.