True a sensor for rainfall could never work, but the plus side if far more accurate wind speed.
I did read its 10x more sensitive at picking up wind over cups which has some weight to push and drag even before it detects wind.
Think the way it measures wind is the strong point and even detects draughts which cups wont pick up.
The whole practical no maintenance and wind are its main selling point.
my own experience of comparing cups(vp2) is the weatherflow begins to fall behind has the wind increases , calm winds are rare events here
As I've stated in another thread, after replacing the speed cartridge on the VP2's cups about 3 months ago (it is different than the old one it replaced), it'll now report 1mph (1.6kph) all day long. I suppose with other software (WL doesn't show wind to the tenth) it very well may display under 1mph. Don't know how much slower one would need.