I replaced my existing sprinkler controller with the Rachio 16 zone system about a month ago. The replacement took me about 15 minutes as you just have to disconnect the wires from the existing system, take it off the wall, put the Rachio on the wall, plug the wires back in, and plug it into power. I recommend either labeling the wires or taking a picture of them before removing them from the existing system. It took me longer to get the app setup since I had to figure out how to answer the questions on soil type, type of grass, shade, etc. that it asks for each zone to customize the watering schedule. Overall I have been very happy with it since then and even use the Alexa integration to turn a zone on to encourage my dogs to come in from the back yard.