Yum. Who doesn't love a nice frozen margarita during the dog days of summer? And they're easy to make, especially with a mix. Just throw it in the blender with some ice, push the button -- whirrrrrr -- and you're good to go. So, don't be fooled by the fancy "margarita machine" on the shelf of the home goods store -- the one with all the cute cacti and coyotes on it.
These machines really aren't that much different from a blender, except that a blender probably is sturdier and will last longer. So don't waste your guests' money on a specialty appliance that does the same thing as an appliance you already have. It's just another thing that will take up space and gather dust.