If Rachio 3 uses weather stations and over 270,000 PWS why wouldn’t they encourage people to buy one or sell their own. See like the more people who own one the more accurate Rachio 3 would be.
Big issue is that owning a pws does not guarantee accuracy. Unless you’d be willing to monitor the data to make sure that sensors did not break and rain measurement did not go too far from calibration, the data from “set and forget” type installation will progressively get worse.
Personally I prefer to use data from people who bought their weather stations to have a more accurate weather forecast & local weather data, rather then those who bought it, primarily, for their irrigation system. Nothing wrong with the latter, but their weather stations are much more likely to go out of calibration or break without anyone noticing.