If a PWS sends Solar radiation data we use it, if not we can get close.
We definitely use forecasts for scheduling.
We allow you to choose any PWS in the nearby vicinity. Sometimes these are highly accurate and you don't even need to purchase yourself.
From my personal experience it won't be that much of a factor when you look at all of the other variables that go into the equation. If we don't get it we have an equation that derives based on latitude and time of year. I think it would all average out.
I don't think it will be that much less accurate.
For our Spring software release we are moving towards a much simpler schedule to setup. It will be the best of both worlds from our flex and fixed schedules. It will adjust frequency and duration each month (water as needed), while also skipping schedules due to precipitation OR we look at ET and see if it can get to the next run.
Hope this helps. Please let us know if you have any other questions or feedback. There will be much more information as we get closer to the software release. We currently have fixed schedules, or flex which waters when soil moisture is depleted. We are refining this and making it easier to setup and monitor for our next release.