I have a Taylor scale which does body fat resistance measurement and weight. It is corrected for age and athleticism.
I had a trainer at my gym do a body fat analysis using skin calipers. After he took the skin fold measurements, he added them together and referred to a chart that had columns for age. He gave my the body fat and it was sort of close to my scale. I asked him why the adjustment for age and the answer is that as one ages, there is more fat stored around organs.
My own experience with resistance measuring body fat devices is that they are very sensitive to hydration.
The most accurate is under water weighing. I had that done about 30 years ago and from time to time I see a van show up at health clubs that does an under water weighing.
In cycling the most important metric is weight - the lower the better. That does not necessarily equate to the best health. I use my pants size and look in the mirror.