I'm not using the containers extension, since it only goes about 20% of the way and then they lost focus and stopped developing it. I think most people don't use it. It could have been a differentiator.
I use it every single day.
It helps open the same website in "Cognito" instead of opening it in Cognito mode.
Plus, as a developer, it makes it easy to run tests using multiple accounts.
I use them every day to separate my SSO sessions and keep cookie hungry websites in check. I could not imagine not having them anymore.