Not only would you need so many, but I would also need it to only run once every two weeks since we are in a drought and have watering restrictions. I guess the idea of this article is not this product but to showcase an application to spark other ideas.
$299 for one sprinker head is very expensive. I would need at least 6 of these for my yard and I don't see myself spending that much. I wonder if they would be able to control costs by using a z-wave controller and the sprinkler as a plain z-wave device. The cost of the wifi, pi subsytems is likely to be the major part of the bom cost.