So you just have to log out and re-enter credentials each time you want to view a different account? And that is fantastic? Doing it several times a day is a pain. Also you only get notifications for the currently logged in account, so you'd need multiple browsers running just to get notifications from both.

Then if you have a mobile device, it becomes even worse as entering reasonably complex passphrases is a long tedious pain. Doing that several times a day is a non-starter.