I haven't, but I do use a chirp wheel for my back and it cracks and pops more then when someone cracks it! I know it's off topic, but it does work!

I love my TENS. My PT told me how it works is it sends pulses to interrupt the pain signals that go to your brain. It also is used to stimulate muscles like a deep tissue massage. So they said to turn it up until it's almost painful and then go down one if you want a deep muscle massage...or turn it up until you feel it and then down one so that it just blocks out the pain.

What is a tens units?

Yes! Used it after my surgery for nerve pain in my arm and hand. It was really helpful for the pain and made things tolerable.