I used to own one, or several actually. First I had the pedal, some ten years ago, but tried to use it with synths. Bad idea, it has a preamp so I would have needed some kind of attenuator to make it work with line level signals.
But then I built a modular system and bought the eurorack module instead. And besides having two inputs, one for line and one for guitars, it's also superior to the pedal in that it has so many modulation inputs (the pedal has one, which can be configured for either an expression pedal or an LFO). If you feed it a lot of different cv currents, it's a wonderful effect. I later sold the modular to buy a custom Serge panel. Sold that, bought another modular system and another Geiger Counter, but all that stuff is long gone now.
Here's an old track I did with the modular, where the Geiger Counter is put to good use, modulated by a few LFO:s and other cv sources. Play loud:
But really my favorite WMD pedal is the Acoustic Trauma, with its crazy self-resonating filters and the ability to make any amp sound like the gear used by early nineties Norwegian black metal bands.