But aren't the devices significantly higher in terms of power consumption than a Raspberry, for example? At least if the laptop has a dedicated graphics card, that's a few watts that the laptop needs ...
It really depends on the laptop. My old laptop takes >20W with the screen off (1 SSD, 1 HDD). I've also seen laptops (with SSD) that take less than 10W. Don't get one with a dedicated graphics card. I prefer a CPU with TDP no more than 15W.
It's going to be difficult to beat the Raspberry, but power consumption can get quite low.