We got one of these some time ago, and installed the outdoor unit outside on the electric meter (as it needs to be set up). It does provide real-time tracking of your electrical usage, though on our large home we have so many cycling motors in heating systems and refrigerators and such that you could not practically test turning on an off a light and see how it changed the load.
The real weakness of the system is that the sending unit mounts outside on the electrical meter, and while it appears weatherized with seals on the battery compartment and reset switch, we had a heavy rain after a month after installing it, and the seals didn't seem to actually keep the electronic dry. The unit died from the water exposure (and didn't recover once dried out). So while it was pretty neat, it only lasted a month, so I'd avoid this unless your meter is well shielded from rain.
In retrospect I'd suggest looking at the competing products that mount entirely indoors at the circuit panel, as anything less weatherproof than the electrical meter itself just isn't going to last.
Andrew