FreePlayPSP: thanks. Keep fighting the good fight. The emperor remains naked, no matter how many people insist otherwise.
Some of the simplest question are also the most profound. "If it really does what it's supposed to do, why doesn't it work on skeptics?" is one of my favorites. Real medicine works whether you believe in it or not. Real anything at all works whether you believe in it or not.
And, yes, I have used TENS systems before, for a few months combined with chiropractic adjustments for chronic back pain ten years ago and following an automobile accident fifteen years ago.
The electrical stimulation provided an easy, mechanical shortcut to precisely the same effect I'd have received from a good massage: my back got all warm and tingly.
(Unfortunately, I couldn't get my insurance company to pay a pretty girl to come over and give me a back rub, so I had to take what I could get.)
Of course, anything that improves circulation will lead to faster healing, because that's how blood works*. And anything that causes mild discomfort will eventually lead to feeling mildly better, because that's how endorphins work*. (Note that Wikipedia's TENS article specifically mentions its use in the BDSM community; in for threes, I'm looking at you. ;)
What this is very probably superb for: Increasing circulation in targeted areas of the body among groups of people who either weren't getting enough exercise before they started using it, or found themselves suddenly unable to take any more brisk walks (because of the onset of the injury causing the pain which led to the use of the device in the first place).
But, again, the device isn't doing the healing. The body is, plus time. The device may be merely giving the natural healing process a bit of a boost.
"Through the miracle of acupuncture, Kissinger had his appendix taken out WITHOUT ANESTHESIA ZOMG" very quickly becomes "a regular old journalist got his regular old appendix taken out while doped to the nines on regular old painkillers" if you bother checking the facts. Why "spoil it" for everyone else? Well, if what you're being told or sold are straight-up falsehoods, then skepticism is pretty, ahem, healthy.
* my source: science.