[This review was collected as part of a promotion.] I tested it one night with only one wire, using only 2 pads. I thought it was kind of weak and I had to keep upping the strength. The next night I tried all 4 pads and I played with all the different settings, and it definitely made a difference. I like the P8 setting, where it cycles through all of the variations, rather than selecting just a continuous cycle for the duration. I also like that you can adjust the time and the strength of each side from this little remote that has a belt clip in case you need to move around. I suffer from bad back issues and the chiropractor uses TENS on my every week. Now I can do this at home as well. I do think it helps a little bit to relax the muscles. I've used the pads several times already. I am not sure how long they are good for, but hopefully they last awhile. I know you can order extra, they include info on how and where to get more.