I owned the first generation of this product from Blue Line Innovations and it gave a good real-time feedback on energy usage. It would calcuate your bill for you and although not exact, it was in the range of my monthly bill. As far as monitoring, i could see what my baseline energy consumption was (things that were always plugged in) and from that I could tell if someone had left a light on in the house. By turning on components individually, you could see how much energy they were consuming.
Now, there is the wifi edition and I’m debating whether or not to get one. The price has gone up due to increased technology.
Check it out by clicking on the pic below: