It is a good approach. I haven't got a chance to use it in a real project.
But, when you use it in a real-world project, these module files may become huge which will be a pain. Then, you may have to refactor it into smaller modules.
But, it also has its advantages. With the normal multi-folder approach, there is an overhead of switching between multiple actions and reducers files. Usually, I define the constants in the actions file itself. I also got pretty comfortable with this approach and don't see a real problem with this approach.
I will try to use ducks approach in a future project. Maybe after that, my opinion may change.