I have had my Gen 2 now for just over four months and have made it well through a hot SE Texas summer. I think I have already paid out the Rachio investment in water savings. The key for me is getting the setup right to start with. I had to custom modify my nozzles for each zone to match what my sprinkler design was putting out. The stock nozzle types were off by a factor of 5 in some cases. The instructions tell you how to do this. Next I needed to adjust the settings (closer weather station, crop coefficient, root depth, efficiency and allowed depletion) to match the results I wanted to see in each zone in my yard. I want green grass and healthy shrubs. I also purchased a hand held Moisture Meter to check moisture levels in the garden & lawn soil periodically. Computer simulations do not think for you!!! You have to match history and what you see to the simulation to get the results you desire. Once that is done, you turn the job over to Rachio and let it do it's job.
I have had to make a few fine tuning adjustments since with extended days of high 90s temp and no rain but I am satisfied that Rachio is dispensing the right amount of water to keep my yard healthy. The real payoff for me is that we spend a lot of time away from home during the summer and previously, I had to way over water with my analog Rainbird controller to be sure drought did not kill my yard while I was away. Rachio has now efficiently taken over that expert monitoring role.
Therefore my advice is once you get a Rachio, spend the time to custom set everything up for your yard zones and sprinkler system and don't be afraid to make changes in all settings to get the results you wish to see. Once that is done then trust Rachio to do it's job and you will save water $ with a green yard.