This is a great cocktail shaker! First, it's a great size and it fits comfortably in your hand, so you feel secure shaking your drinks without having to grip it in both hands. The double wall helps to insulate the container so that your hands don't freeze while mixing your drink with ice. And the built-in measuring device is great for bringing with while traveling! 
I recently started making my own margaritas at home, at this has been an invaluable tool to making the best margaritas I've ever had.