I don't have a hand held device, but do have a body fat scale. I can just weigh on it, or do weight and body fat. Works by pulsing a small electric charge through the body to measure. I agree it isn't truly accurate. But over time, I have gone from 38 % to 32%. So it is useful to me personally, as a reference to my personal progess. I don't know if either measurement was anywhere near my actual body fat percentage, but it has consistently gone down with weight loss and exercise, so it is reflective of change.
zen and the art of weight loss, finding the true path of en-lighten-ment