Never heard of such a thing, pretty cool! (you may have just cost me $32!!) Amazon reviews look really positive.
I just recently starting trying to conserve since my new power company sucks ($19 monthly fee and more expensive than my old power company). So my bills went from about $35/mo to $75/mo (lots of air conditioner usage). I downloaded an app from my power company which shows my kWh usage per day, which is really handy. That lets me know approximately how much more I'm spending each day when the thermostat is set on 74° vs 76°, all else being equal.
Back to this Belkin - I'm really interested in how much my spare 1991 refridgerator in the garage will cost (currently unpluged). I can figure most items out just by doing the math, so I'm still contemplating the purchase.