I haven’t been able to figure out what problems people have with HomeKit support. Seemed easy enough and seems reliable enough to me. I do know they were unable to get it working on prior generations do to code complexity.
I do have it working on my system. I don’t really use it, Home isn’t sophisticated enough to do much other than quick-watering a zone and real-time monitoring.
The difference is the rachio controller and app are set up to do configuration and intelligent scheduling, while something like Home or Alexa really can only monitor its state or tell it to run for a while.
That said, it is good for showing off to visitors.