It met all my needs for multiple profiles. I use it to have multiple concurrent sessions for different sites (eg: one AWS account/role per container).
[1] https://addons.mozilla.org/en-US/firefox/addon/multi-account...
Where I work we are required to have 2-3 Microsoft accounts for security separation. Account containers makes it possible to interact with virtually unlimited profiles all in the same browser window. No need for in-private browsing or multiple widows of chrome or edge, it just works. When you have it configured just right it's a thing of beauty.