Don’t know about the UK, but in central Europe it’s common for houses to get three phase power that can then be used on 400V three phase circuits and gets split (ideally evenly) into 240V circuits. And the fact that the phases have effectively zero coupling means that you also need to just try the adapter to find out if it’s going to work or not unless you happen to know how exactly your house is wired up, just like with split phase power.

Apartments usually get a single phase though, but IMHO it’s also less likely that WiFi won’t be enough there, so it’s questionable if that’s even a point for powerline.