It can work. I installed one in my dad's old house and it worked like a charm. But when I went to put one in my house a few months ago, I did get it to work, but I had to try various locations of ethernet jacks and power plugs to find a combination that both worked and usefully extended my WiFi.
I tried one in my old place and it was really poor - much worse than congested WiFi (dense neighborhood in a large apartment building).