Provided you follow the setup for the devices like an ABSOLUTE PEDANT they will do what they are advertised to do - ish!
The problem that you'll face with standard range extenders is that they tend to reduce the throughput of YOUR WHOLE WIFI NETWORK by half
In many cases, something like the TP-Link TL-PA8010PKIT which is a powerline and WiFi combo may be a better bet (there are some nice Devolo devices too). If you can, try to keep powerline adapters a few feet away from any wall phone sockets. *Again following the instructions like a pedant applies!
