Broddr's review, describing how you could use a pair of these to run two ethernet connections over a single wire is incorrect. There are splitters which do what he describes, by separating out the unused 4 connections into a second socket, and for which his description is absolutely correct. This product is not one of those splitters - or at least the ones I received aren't.
These splitters connect all 8 connections between all three sockets. So at point A in Broddr's description you would effectively be connecting the two sockets on the router to each other.
This _can_ be used to "split" a socket into two, provided only one connected device is active on the network at a time. In my case I'm using it to connect an XBox360 and an OnLive box to a single socket, which works fine provided only one device is powered up at a time.
But to be honest you're probably better off searching for a network "economiser" (that seems to be the term widely used on Amazon), which _is_ the sort of thing Broddr described. You'll need a pair of them, and then Broddr's description is spot on.