The idea

The idea behind a detox footbath is using the electric current to draw out toxins from the body. The machines used for this, do not require you to only use the feet. The main reason most use only the feet, is due to comfort and easibility. Most machines can be used in the bathtub while the full body is in the water as well. However, I would suggest you bleach the tub after use. There is usually a ring left in the tub after you detox.

Personal use

 I have personally used the detox foot bath as well as my whole family. I found using a detox footbath has reduced my seasonal colds. My son has a high metal count and the treatments helps his body releases these metals. This was the pirmary reason we ended up buying a machine for ourselves. We purchased one for $600.00. Due to the continued cost of treatments, this was a better deal for us. Owning one, also allowed us to use it when we had the time (as opposed to scheduling) and it was utilized by the whole family. 

 The Scam Idea

Many will say this is simply a scam and does not provide any use for you. I cannot speak for all, however, personally, I have seen improvements in my life as well as my family. The other issue is due to the popularity of the detox phenomena, alot of ripoff devices have flooded the market. I would caution and do research prior of purchasing a detox machine.