That isn't true - you say yes/no the first time and then it's automatic. Works great for me.
I create a container for every service I want to stay logged into and whitelist the specified sites with Cookie Autodelete (which is container aware), then auto delete all other cookies on tab close.
Also, I'd love to do this in my bookmarks, instead of having to visit each site and set the container one-by-one.
I have some sites that I almost always want to open in a specific container. Except when I don't.
I suspect this double-confirmation is for people like me: I can chose between "always open this site in this container" and "always suggest opening this site in this container".
I thought containers were clunky too until I went looking for bug reports for the functionality I wanted (always open domain in container) and found out I just wasn't using them right.
I'm actually really impressed with how polished it is given the complexities it entails
Not sure of it or something similar was referenced at some point during the extension install process.