I've been using this since shortly after it was released to separate logins to the same site by different users; for example, when testing a user account while logged in as an administrator. I also use it to log in to Office 365 with different user accounts while supporting multiple clients.
The recent UI change did seem inconvenient (more a matter of interrupting the flow) but seems to have been a necessary compromise to allow additional functions. Instead of left-click, left-click on the icon, it's right-click, left-click on the "Open a new tab..." button. Change is good, humans are capable of learning new ways of doing things without whining.
The new font in the list allows me to see all of my Containers.
One suggestion for a future enhancement would be the ability to sort or manually order my list of containers.