The Boston Cocktail shaker is the shaker of choice for cocktail makers and professional bartenders. Why? First, it’s fancy looking and makes you look like a professional in front of your friends.
However, the Boston Shaker has a practical use as well. When building a drink it’s nice to show your customer/friend/family what the drink looks like as it’s being created. This allows the viewer to know exactly what’s going into the drink and what ratio. The second half, the metal half, is where you’re typically going to pour the contents once the drink is shaken.
If you read some of the reviews for the boston shakers, you’ll notice people say “mine didn’t ship with the top,” because they don’t understand the Boston Shaker is a two-piece unit.