"I'm curious to know how the kill-a-watt actually works. For $20 I'd be surprised if it gives an accurate measurement of reactive loads. They claim "up to" 0.2% accuracy which would be easy for resistive loads and they know no one is likely to dispute them anyway."
Yeah I'm suspicious as well. 
I found two contrary claims, one on consumer reports - Consumer Reports Magazine 2022
And another comparing it to a fluke 1735 which paints a less rosy picture - http://forums.anandtech.com/messageview.aspx?catid=84&threadid=2147352&enterthread=y