I'm not znpy so I don't know why they don't like containers.
But I prefer profiles myself, as I have different extensions in different profiles and I get the two completely separate instances of Firefox, while containers are just separate tabs instead.
I don't think containers are awful though, they are just less useful for my use case than profiles.
I sometimes have issues with the profiles too though. If I have both profiles running concurrently and I click a link from a different application, I get an error that "Firefox is already running" and it freezes up the window with my primary profile.