Hi Roger, and welcome to the forum.
I have a TENS unit from RS Medical and I love it for my back muscle spasms. I use it when I have to drive over a half hour, or when I've picked up the grandchildren too much causing next morning pain. I love the portability! It's battery operated.
I've tried the unit for other kinds of pain, but it seems to be limited pretty much to muscles that cramp up, causing pain. I don't like the wide belt part of the unit - too bulky, although easier to put on and off. The belt is too short if you have much of a waistline, but they supply an extender. I like the individual pads better becuse I can put them farther apart and more individually place them.
I don't think of using this as a daily "treatment" as talked about
in the reading material. It's no cure. It does do a good job for me relieving spasms after they've started, but I don't know if it would ward them off. I do put on the pads if I'm going to do something that I know will start the spasms. That seems to work.