This is the most effective, and simplest, wifi extender I have been able to try out in my long, thin, heavy-brick Victorian house. The router is at the front, downstairs, and I am at the back, upstairs. I barely get any signal normally, and when I do it is maddeningly slow. Cue this little box, which looks essentially like a standard plug (a little bulkier) without a lead.
Set up is a real doddle. You plus it in - I put mine in a socket approximately half way between the router and my room, downstairs - and then you connect to it from your device. Go online and enter your wifi key - you do need to reconnect to your pre-existing signal - and there you are. I now typically have 3 wifi bars on my MacBook, sometimes the full 4 - and speeds have been transformed.
Belkin seem really to have cracked it with this model, beating their own offerings from a mere year or two ago. Highly recommended to alleviate hotspot woes in your home.