Don't worry Trumpy -- I asked the same question when I first joined ECN as I'd never heard of a Wiggy either!
The low impedance makes the solenoid-type tester much better for testing whether a circuit is actually energized or not.
DMMs are so popular these days, but the high impedance (typically 10 MEG) means that capacitive coupling effects can give rise to all sorts of confusing readings. If you look back through the archives you'll see several threads relating to this.
