"Wiggy" is a registered brand name of Square D. This solenoid style voltage tester was originally made by a company called Wiggington. Klein tools resells this Square D tester.
Solenoid type testers have much lower impedance than electronic and neon style devices. One advantage of this tester is the ability to not indicate voltages caused by leakage currents and capacitive coupling currents (these are some causes of digital meters indicating voltage even if they are just "laying on the table"). A disadvantage of these testers is, the low impedance causes high inrush and "chattering" currents which can be damaging to electronic switching devices.
