Some issues with containers:
* It's way too easy to open new pages in the wrong container, and you can't convert an existing tab into another container. By the time you've opened a tab it's too late. Solution is to copy URL, create new tab, paste URL, which is a lot to do.
* There's no "New tab in same container" keyboard shortcut or button.
* If you click on a URL in a different app, or from the shell, you get a new tab in the default container.
* There's no way to designate an entire window or macOS space to a container. I have all my work stuff in a separate space, and no personal stuff should interfere. Similarly, if I'm already in a window full of, say, Google Cloud-related tabs, I don't want to clutter that window with containers.
The idea is great, but the implementation is nowhere close to being practical.
Chrome's profiles are too heavy-weight, but it has the right idea about the ability to couple window with profiles, because windows are "collections of tabs", and the most natural-feeling container of pages.