I assure you that's not my motivation at all. I'm not an expert in that field so I tend to trust the metrics used by the health professionals I encounter.
> BMI is widely regarded as totally obsolete
That is not my impression at all, but again I'm not a subject matter expert here. If you have reliable (ie academic or medical) sources I would be interested in learning more about any current preferred metrics.
What do you have in mind? With a bit of searching I haven't found much that's cheap. (Obviously you can take some tape or caliper measurements to improve your numbers but that's neither new nor particularly accurate.)
First, there is a fundamental constrain that it measures impedance only through legs and a little bit of belly, but no upper body (at least here in .cz, no consumer-grade scales have hand electrodes). I do road cycling as the only sport, and therefore get extremely skewed results as I have strong legs, but the rest of the body is much weaker.
Second, the measurements are almost non-repeatable. You get tens of percent difference across measurements, god forbid if you suddenly have moist feet etc. However, both scales used firmware cheating to mask this noise: once you set up a "profile", it will remember the initial value, and then change the following measurements only slightly. However, set up a second profile (preferably with a slightly modified age etc. to prevent advanced firmware cheating) and you get completely different results.
It's imperfect, but generally correct. More importantly, it's easy to measure. Accurate except for outliers isn't as much of an issue as you think it is, especially as these are generally already accounted for by its users.
It’s well understood that BMI is totally wrong for athletes or anyone remotely muscular.