I don't think it is a bad measurement of energy for transmitting a scale. It was an actually used nuclear bomb and with enough understanding of its power and consequences in our current culture. Your message have a target public, and that target must understand it properly.

A Tsar bomb or a long number with an unit attached won't be as graphically understood as this one. Scientists may grasp those numbers, but they already know how bad this is, you must reach everyone else.