Edit: I've removed one point and added a new one.

This should be excellent, but in reality a few bugs make for a frustrating experience.

The containerization really helps when working with multiple contracts for multiple work accounts, allowing several Office 365 sessions to be signed it at a time.

I love the facebook container, as I use facebook once in a blue moon, and love that this keeps it in it's own tiny bubble.

There is some inconsistency though:
1. By default firefox opens with no default container. This means you have to open a new tab in the correct container, before you start browsing, then close the original tab.
2. If you use the keybord shortcut to open a container, it does not prompt you to choose a container, it opens an uncontainerized tab, forcing you to either reopen the tab in the correct container, or use the + in the bar, which is significantly slower from a workflow point of view.
3. You cannot set home pages per container. By default, my "work" container (for my company) always accesses the same site, with all tools launched through that site. If i could set that as the home page for my work container, then it would save me a dozen clicks and keyboard presses 30-40 times a day. Add that time up.
4. You cannot assign a book marked site to a container, as above this would vastly improve matters. THis would make the Top sites useful, as clicking them would immediately take you to the site in the correct container, likewise would mean technical research would be faster as you would not have to open the correct container by clicking the +, then choosing the container, then selecting the bookmark.
5. Turn off the No Container option. Now I'm using containers, all my workflow fits into one of the configured containers, so the no container option is obsolete.
6. Make the option to Sort tabs by container a permanent setting, rather than a one off setting. I end up using this option several times a day to regroup related sites running in the same container together for organisation, but it's frustrating that as soon as I open a new tab of that container it doesn't group this with the other tabs open.