I've heard that a lot of people find these to be very efficacious -- I'd be interested to hear your thoughts -- how well does it work?
I guess it depends on your problem and your body. As withh all things medical YMMV. My chiropractor remarked that I always responded well to interferential treatment (not strictly speaking TENS) and that I shuld perhaps get myself a machine. Ones that include the interefrerential are not quite as common, but I did manage to find a few.
There are 40 "modes" on the machine. Only 4 are interferential and it is possible to adjust both the frequency and the intensity. I am not quite sure as to which is the best, but hey I am not paying for the time, so i run it over 3 or 4 interferential modes for an hour or so. It certainly helps me and is sometimes even soporific. Maybe it is just psychosomatic, but it works for me. The whole thing is portable, so I can stick it on and wonder around or simply lounge in front of the TV and even doze off.
I should add that I have even bought an inversion table, but it didn't seem to help at all.
I recently bought myself a TENS machine to help keep my back in order. I have a disk that keeps slipping out of the top ten. As Mad magazine said, you know you are getting old when your back goes out more than you do.
Anyway there is some cautionary wording not to apply this across the base of your neck as it could interfere with the nervous system. It didn't seem to occur to them that someone could use it on their brain. There is also a warning that the unit can only be used by qualifed medical personnel- shows you how good the warnings are.