If you check the "Always open this page in this container thing" - then it prompts you with an "are you sure you want to open this page in this container" every time you go to that page which is very annoying. Edit - this is not true - there's a checkbox to "remember your choice". I don't know why I didn't see it.
They are error prone enough that they aren't good tracking protection. Just use ublock origin or a similarly good privacy plugin to globally block as much tracking as you can.
The facebook container eliminates some of those annoyances, but only for facebook.