First saw these in work (work in electrical retail) and they seemed like a great idea, and they are!
However, they are flawed. They do the job but with a few little issues...
In smaller rooms (like mine) you get a slight ghosting of the other players image.
The image you view is also slightly out of proportion, squashed one way or another as it is stretched to fit the screen and no amount of adjusting the picture settings makes a difference!
Don't let this put you off though, if you just want a quick and easy way of having two players with full screens then go for it!
If you're huge on having your picture perfect then leave it until LG update the tech a little, I'm hoping they release a software update that will allow you to adjust the picture more to size as the ghosting I mentioned is barely noticeable when in action.