I've got the devolo wireless extender. It consists of a standard homeplug that plugs into the router (wired) and a socket near the router. The homeplug at the other end communicates with the first one over the leccy cables. It also sets up its own wifi network and you log into that. It doesn't work off the wireless bit of the router. It is wired (over the leccy) to the router, and then sets up the wifi in the location where you plug it in. Obviously, you can connect multiple devices to the wireless, so it might save you a few quid over buying separate wired homeplugs.
Hope that makes sense. Dense day...
