My family lived in Phoenix, AZ since i was 6, and he had an Evap Cool and a traditional AC. Early in the summer the Evap works great and is way cheaper. Once it gets too hot or too humid, you switch over to the AC. The fun part was, my Dad would hold off switching as long as he could, and kind of compete with a friend nearby to see who could "stand it with the evap" as long as possible.

The hardest part i couldn't ever keep straight, was with the Evap you need doors open and with the AC you close them. i would get it straight by the time he'd switch over to the other system..