They also aren't cheap. They sell inserts you can shove into each cubbyhole that are also mostly cardboard and toy-like hinges and handles.

A 4x2 Kallax is 99$ and if you add a few inserts it easily goes into 200$. You can buy a much sturdier and larger metal wire-rack shelf for the same price and it will hold a lot more. (Home Depot)

The Kallax is a nice presentation case for displaying things, it's not great for storage.