I’ve seen similar functioning products before but they are bulky plastic things that cradle the entire carton of milk or juice (like this one for example). This design for a milk carton handle by Minna, takes a more minimalist and stylish approach. It’s made simply from two joined pieces of wood.
The other advantage this has over the plastic cradle types, besides just looking better is that it can attach to any size carton. Also it looks like you can easily clip it on and off from your milk carton, which means you can use one for multiple beverage cartons in your fridge and you don’t have to keep them attached all the time, thus saving space. Not sure of any availability- the site is from Japan, but I like this product, simple, elegant, and functional.