Easiest device to use, just plug in and plug electronics, etc. or multi-outlet extension cords into it. Push buttons to view electricity usage details at the moment and since you plugged whatever into it.
Tried two of the Kill-A-Watt monitors, and they provided solid proof that my roommate is wasting tons of power every day, so I just shove a page of all the useful data the monitor provides in his face whenever he attempts to blam me for the increasing electric bills (My power consumption = 28 % of the total electricity, and he uses 72% of it. Hmmm.
Seriously, I've cut my electrical consumption back to 22% thanks to the info the Kill-A-Watt tracks and displays in real time. My roommate says if I ever bring another KILL-A-WATT into our place again, I'll end up paying the library for the cost of one being lost...or try to get SPL to take a bunch of pieces of a Killed-And-Wrecked unit back; funny roommie, huh?