Yes, the system work by installing a litle ring-like device around the cables which measures the power being used, probably using the magnetic fields that the current generates. I have installed it between the mains point and the electricity meter, so technically it should measure the same thing the meter does. There is a battery powered emitter which you need to put about a meter away which then sends the data to the receiver. We have a high house and it works everywhere. It's a lot more convenient than the meters you plug in the power socket, but obviously it also costs 4-5 times more.
-- screen --
If you have a 17" CRT or a 19" which you dont use at high res, buying an LCD screen (around£100 nowadays in the UK, cheaper in the US) probably pays for itself in a year. At least in a country where energy prices aren't heavily subsidised. If you want 1600 res the screens cost a bundle more, and I suspect they also consume a bit more so the savings in energy probably can't justify buying one.
-- a little side rant --
My laptop, which got stolen in October (dont get me started how the insurance company still hasnt sorted the claim out!) had a gorgeous 17" wide screen that did 1900x1280. Now I *would* buy a screen like that but they don't seem to sell those as desktop units. It seems I have to buy a 20" screen to get 1600 res. The smallest 1600x1200 I found is http://www.ebuyer.com/UK/product/92683
which is actually quite tempting (would have put a link to the manufacturer but that site seems broken).
You can tell that the manufacturers have established than when consumers and IT managers shop for screens, the "prestige" factor seems to be in the screen size, not its resolution or contrast ration or anything else. This is of course not the case in notebooks where screen size is also a weight issue and where it's worth doing a 17" high res screen - they clearly think that the same screen on the desktop would not see against all the 1280-1024 19" screens. Shame, I would buy it.
You get the same thing in digital cameras where clearly it seem the number of megapixels is the "prestige" factor, even when there's not that much of a difference for normal users between 6mp and 10mp and other factors would really be far more important... people seem obsessed by size!