The UX is horrible. This extension have a design problem with the "No container" state:
* You can move a website to a container, but you can't take it out of a container.
* Moreover you can't choose "no container" as default state for a website if you have chosen a container previously.
* Also the extension always remember your last container for a website and you aren't able to disable that "feature".

Please review the "Cookie Swap" extension, which is much more simple (but it has some bugs unfortunately).