Scaledinstruments.com is where I buy my weather stuff. Ryan is a great guy.
Solar radiation like UV radiation can't be accurately forecasted and assumed. For example, most weather services forecast the UV index. But don't take into account the atmospheric influences like water vapor, dust, smog, etc. The best way to get solar and UV radiation is to measure it physically with a sensor.
I think the challenge for Rachio, is that of the thousands of stations, only 1/5th of them actually report solar radiation. If you live in the country the closest solar radiation sensor maybe many miles away. The only solution as many of us find out if to purchase the proper equipment ourselves.
I definitely support Rachio Iro in using PWS solar data for ET readings. In addition, the solar readings or alternatively sunset or sunrise information can keep from watering in strong sunlight which as we all know can burn foliage.
Hope this helps.