Frank has never needed a WiFi extender in his home, but his girlfriend's house could use one. So he installed one, but it doesn't seem to be doing much better. Leo says the reason is because an extender has to spend half it's time talking to the router. They can't speak to both devices at the same time. Mesh routers, by contrast, have a dedicated backchannel that is always on, that talks to the router without impeding the bandwidth speed. They can be a bit more expensive depending on how many satellite units you need for the house.
Another option is powerline networking. This is where you plug the extenders into the wall and it uses the home's electrical grid to transmit data all around the house. The best about it is, that while it isn't as fast as wifi, it's more reliable because it's wired. TPLink makes some of the best and affordable units.