It's literally a button, with some extra stuff attached to it. The only requirement for a button is that if it's accessible to the person trying to press it (no pictures posted of that, feel free to assume). But, there's intentional inaccessibility built into this project, so that may be an intentional goal.

Thats's the great part about home assistant though...anything that can change states, with intent/meaning, is waiting to be tied to an automation.

I'm guessing they already had the plug (I myself have a small stockpile of extra Z-wave/wifi/Zigbee devices for when I inevitably need/want to hook something up), so there wasn't a need to buy something else.

OP had a socket with a button and decided to use it as a button. Yes button works, but you don't have it, like OP, then socket like that will do. As a bonus, you can put a light bulb that indicates the state.

I think this button is powered by the outlet.