It's usable I guess.
The main issues it has are:
1. when forcing a site to always load in a specific container, subdomains are never included. There should be a way to include them.
2. After setting a site to always open in a container, there's an extra dialogue that appears the next time you open that site, which can sometimes render the browser inoperable.
3. It requires a keybinding even if you don't want it to be set to anything.
4. You can't make it so certain sites load in the default container.