I cannot speak for the 'ease of installation', since I'm merely an architect, not a roofer, but I can tell you these points:
1. If a metal roof is not properly installed, you will get "oil canning", a popping sound as the roof heats/cools with sunrise/ sunset/ shade/ shaddow and sometimes even with wind.
2. I believe there are specialized tools for crimping and bending the "battens" or "standing seams", depending on which kind you choose.
3. There should be no difference in heating/cooling costs if your attic is properly ventilated. If it's not properly ventilated, it doesn't really matter which kind of roof you choose.
Your stats say you're in Arizona? Is that where the house you're re-roofing is located? I'm curious because one of my clients and I just spent a lot of time researching rain-harvesting systems for a house in the Texas hill country.
Turns out a metal roof is the best option for catching rain water. I know AZ probably gets even less rain than the hill country, but y'all are going to have the same water problems that they are.
If you think you might be interested in something like that in the future, you should consider buying the metal roof that doesn't come with an oily/chemical film on it (most do have this as an added layer of protection against corrostion).