I installed my own sprinklers and drip - 22 zones of it. A Rainbird controller was going to be nearly $300. I went with a pi and loved it. Then came the real problem - I put the home on the market and ended up replacing my pi with a rainbird for the next people. Why? I kinda wanted to keep my setup and buyers didn't know what to think of it.
After I swapped it out I missed quite a few things - controlling it from my phone, from home or remote, being able to pull up a graph and see how long each zone ran. I wasn't in the mood to get up at 3am to see if the rainbird was working so I crossed my fingers and hoped it would work at least until the house sold. Setting up all my zones was a lot faster on the pi than it was with cranky dials and buttons on the rainbird. I won't miss it.