If seems this should make obsolete the setup of having a separate computer (e.g., old laptop) to isolate Facebook properties, or am I missing something where a separate machine would be advantageous?
(I avoid FB like the plague but may need to use it for some biz uses where they effectively host too large a share of the intended market)
Depends. Either you need to guard against e.g. fingerprinting the GPU, in which case you still need a separate machine, or you only need simple separation of cookies and the like, in which case you never needed that and could just use separate browser profiles. But yeah, I think in the latter case containers should work, though if it matters you should double check what exactly they do and don't separate.