OP, do you mean the extenders that use your mains cabling to transmit the Wi-Fi signal (powerline adaptors, I think), or the plug-in Wi-Fi repeaters?
I’ve got a TP-link Wi-Fi repeater type thing, like this:
and it’s a bit ‘meh’ to be honest, but is a few years old so perhaps things have moved on.
It instantly halves your network speed for anything connected to it, by virtue of how it works and it doesn’t seem very powerful.
I bought it to extend the Wi-Fi into our garage. I originally plugged it into the kitchen socket nearest the front door and it must only have about 15ft to transmit but the signal wasn’t very good.
I then realised that there is a socked in the understairs cupboard and because the garage is attached to the same wall, it would almost be directly adjacent to where I need the signal (but admittedly through a brick wall). This works much better and I get a good enough signal for Zwift & Spotify.
If buying again, I’d go for the powerline adaptors.