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.
The thing you want to do for your application is probably measure power the same way the power company does, as inaccurate as it is, because that's how you bill is calculated after all. 
I think your project is great! It really shows what we can do with inexpensive hardware. Keep up the good work.