Ours doesn't even show real time usage. Only averaged per hour, so you can't learn anything useful at all.

Apparently, they do make a difference if they show the data you want and are in a place in the house where they are easy to see.

We bought a little plug meter many years ago, and that had two instant effects. We got rid of a CD player that was using about 30 W when not in use, and an old, inefficient fridge followed not long after.