Except that the behavior of creating a new tab via the + button vs. CMD+T (in Mac) is that one of them creates a tab in the active container and one of them does not. This is a dealbreaker for me and kills the hype.
Check out the "Sticky Windows Container" add-on.. it makes the container of the left most tab the default for that window. It's a pretty decent way to manage multiple default containers.
https://github.com/mozilla/multi-account-containers/issues/3...