I don't have a flex belt or one of those weight loss things but I do have an interferential machine. A tens unit is basically the same thing but may cause pain for some people. It has four leads where electricity goes through pads. You criss cross the wires over the area that causes you pain. I have been told the weight loss machines are basically the same thing. It has done nothing to tone but I absolutely love it because it takes my pain away. I refuse to take pain meds.
LOL I would turn it around and use it on my back, throw it around my shoulder, etc. I would say it would be like doing isometric movements. Your muscles do contract esp. if you crank it up. If you want/need to know, my inferential unit's price tag was $2,000. Not sure what a good price would be for the flex belt.
I just googled them. You only get 3 pads, not four like I have. The belt doesn't allow you to place the pads where you want them. The reason four is used is because of how the electricity flows. You can just use two with my machine but four works the best from all the studies. I would say you'll be replacing the pads at least every two weeks, you can stretch the use of them by cleaning the area with alcohol and getting the pads wet with water to make them more sticky.
I probably confused the issue more than helping. Good luck.