It pretty much is that simple. I have a 3 of these, one in my bedroom, one in the kitchen and the main broadcasting box in the living room. I have it plugged into sky, my DVD play and a Video.
The good point of these it that you just plug in and play. The bad thing about them is that you may find it gets interference from Microwaves, wireless networks, remote control cars etc. The Microwave one is the killer as it becomes totally unwatchable.
My recommendations is that if you by them, don't buy the ones that run on the 2.4Ghz spectrum. Look for ones that use the 5GHz and this should stop the interference which everything else uses.