I've seen these scales in sporting goods stores. I just assumed it was a gimmick to sell the scales for more money. Are these scales accurate? How do they figure out body fat? Are they worth the extra money?
I don't know the accuracy, but they seem to reflect what I see in the mirror. You'll have to do your own google research to know for sure. Tanita seems to be the big name.
It works by shooting a little electric current through your body. That speed, measured against your height, sex and weight (you enter your height and sex manually when you set it up)gives a body fat percentage.
I recommend the scales that have settings for two or more people, otherwise you have to enter your sex and height manually each time.