Depends.
Those body fat measuring scales are heavily inaccurate by design. The scale pretty much measures your body's impedance from one contact to another by applying a very low metering voltage. – Let's keep in mind that electricity always will take the part of least resistance.
If you buy any of those scales with only footplates it will simply measure the impedance between your left and your right foot, which will inevitably ignore the entire upper body.
They have just calibrated the scale of their measured impedance to extrapolate from the "fat" of your lower body to give a hint to how fat your upper body is. This of course only applies for "averagely built" people.
If you have skinny legs and a fat gut or fat arms, you might end up with a body fat, which is way too low.
You can observe this phenomenon with older men. Despite not exercising at all and carrying around a significant beerbelly, all whilest having skinny legs, they might end up with a body fat with 15%.
My brother's girlfriend bought a Withings scale for christmas two years ago and we let our dad step on it. He has the physique I described above and was measured to 15% body fat, whilest my brother and I were both in the 20-25% region, looking way leaner than my dad.
The only body impedance measuring scales that kind of work are the ones with a tethered handle, which are contacted and you have to grab and hold up in front of you. The quality ones of those run different measures:
And those measurements get averaged out, which yields a higher accuracy.
In my humble opinion. Those scales are utterly useless for women, due to the largely varying breast sizes, which aren't taken into account at all.
However if you have implants in might even work, as the measurements only takes into account the impedance between your legs anyways ;)
Cheers