They aren't very accurate.
Also consider that body fat testing on similar devices is going to be even less accurate on a stand on only scale. They tend to "bias" lower body in the readings in the same (opposite?) way that hand held testers may bias the upper body readings.
Even the more expensive Tanita scales with handles or something like an Inbody are not terribly accurate. I should be honest in mentioning I have used both with clients (and still do) and for some broad sweeping changes they can be helpful with very general trends, but I wouldn't want to have one in my house measuring me every time I stepped on a scale (I feel it would turn into a mind-F).
Maybe if there are other components of the scale you want they could be worth it, but not really for the body fat testing. IMHO you'd be better off with just a basic bodyweight scale (mine is like $15?), again unless there are other features I am overlooking that you may feel you benefit from!
Sorry for such a long post.