I live in a place that is very hot for a good part of the year. Temps can easily reach plus 40 c (105 f) for prolonged periods of time. I am not sure heat pumps will work well in my environment. They would have to be oversized to handle the hot periods and as a result would be massively oversized for the couple of months I would use it to warm my house. My opinion is they are great for 50/50 climates where they can be sized properly for summer/winter. In the South AC Systems/Furnace will perform better since you can size each system for summer/winter properly. An example of what I am talking about is in Northern States you have a severe winter that would require a large heat pump but in the summer the units cooling will far exceed what it should be and would create problems for the living environment (dampness, mold, etc).

I suppose if you live in an environment where you only use either the Heat or Cooling but not both, it would be ideal.