> is this really more effective or smoother in terms of workflow than just using standalone neovim and tmux? No, but this would help fill in the gap that tmux lack for some use cases. So, it would all depends on what are looking for from it.

With (neo)vim as terminal multiplexer, you would have a totally different ecosystem where you can integrate various plugins to it. Like tmux has TPM, (neo)vim would have vim-plug (or many more plugin managers) to help integrate another plugins and tailor to your setup.