The problem for the duo is a design choice
By keeping the looks of the zero and the lid this creates two problems
You can see the beans and it’s not a tight seal so bits escape
On the zero it’s easy to sort because the burrs have a center bolt
The duo you don’t have this luxury, and as the hopper can hold 100g of beans you can’t just have a cap, you also have to feed the beans at a certain rate.
When you look at the timemore it popcorn but has a tight lid, every single dose grinder popcorn. You just generally don’t see it.