My chiropractor uses an adjusting tool that looks like the hypo spray on the old series. He laughed when I told him. Originally it was used in dentistry somehow.
When I was going to one, he used one of these as well. I viewed it as a "clicking" device. Probably with a spring from one of those ball-point pens, it was designed to make a soft "click" noise when button was pressed.
Seemed placebo-ish to me...
But, I'm no Chiropractor.