I've borrowed one at work. I was trying to use it to determine the real-world load I was generating with some servers, but it didn't work on the normal power cable. I had to go to the panel and measure there. But that's not as granular as measuring each cable. I had to estimate that each one was drawing about the same amount of power.

The one I'm using is pretty much of Sears quality, I'm guessing. It's an Amprobe analog deal. It looks like it was made in Taiwan by retarded monkeys, but it seems to work.