Note that it is OGE hover so some distance below the disc - not the same as standing directly under it in a low hover.
It is useful in assessing proximity to VRS since, if you know your downwash speed you know where the likely critical RoD is.
If you know a better way then post it.
I don't know a better way, but I do know from looking down from 10 meters it's a hell of a lot more than that