That description isn't accurate at all. 1 to 3 seconds will cause pain, nothing more. If the attacker "drops to the ground" it is purely psychological trauma and probably won't happen, especially if he's pumped on adrenaline and/or some narcotic.
In order to prevent the muscle you touch from functioning, you need to apply so much voltage and time (15-30 seconds) it will cause permanent damage. That's why most people recommend pepper spray, not stun guns, for a non-lethal deterrant. Plus, who's gonna stand there for 30 seconds and let you shock them?
But of course, pepper spray just doesn't flat out work on some people, and it will not stop someone who can deal with the pain and keep on going. And then of course there are nacrotics and alcohol, and most violent crime is committed when under the influence of either (or both).
If you want a self defense option with a flashlight, I'd recommend a Glock with a flashlight mounted to its rails /ubbthreads/images/graemlins/smile.gif