very useful

Highly recommend this - great for managing multiple accounts (e.g. mail)

does the job! Improvement would be to create a new container tab from the context menu of a tab (right click on tab-title)

Excellent.

I've found Containerise to be a way better addon than this.
MAC for me takes like 10 seconds to load the menu, Containerise opens instantly.
Adding a website to a particular container is quite an annoying process, since you need to scroll the container list, and there can be dozens of containers there if you use Temp Containers addon.
Meanwhile, in Containerise adding it is very easy - you can even edit the config in form of text directly, you can also import/export the config in the same way, as plain text.

A fundamental feature

It's hard to give a review for this, because the effect can be hard to see. However, being able to separate different websites into different containers is really useful for when I'm multi-tasking and trying to use multiple accounts at one time.

Also, I think I've noticed less scarily intrusive and stalking ads after separating the accounts and cookies into different containers.