The better ones, it is just another name for a refrigerator, and they work as well as a refrigerator. Some I've seen offer option to use as either a fridge or a freezer, have not seen one to do both at the same time.
Others really are just coolers, with limited capacity (-20F to -30F from outside temp) and if you are in really hot weather, you are better off with an ice chest, which will bring the melt water down to 32 F so long as there is ice left, regardless of ambient temp. Yes, they do go through a lot of ice, when it is hot. I've kept ice for two days in Oklahoma summers, 5-6 days in Michigan with the cooler in the shade.