--device you are referring to is the Rebuilder, which, like many therapies discussed here and elsewhere, had a vogue for a while, did benefit some people, but wasn't consistently beneficial across all types of situations.

It was basically an electrically enhanced magnesium salt bath for the feet. Certainly the biochemcial idea was interesting, in that the functioning of the nervous system is electrical, but the results were rather mixed, and the unit was rather expensive.

As far as TENS placement goes, that is very individual. Some people like to place the pads right on their painful areas, others slightly above them to get the current/vibrational effects moving down and through the area of pain. You'll probably have to play with the placement to find what works optimally for you.