Yep. Specifically, the temporary containers keep me there for web dev stuff. People will always recommend profiles in chrome, but that can't replace a single hotkey to spawn a temporary throwaway container.

How is that different from private browsing?

I can have 3+ different temporary containers open at once, each with a distinct set of cookies, whereas private browsing gives me only one extra cookie jar.

It's massively helpful for testing interactions between users.

At least on my chromium variant each private window (not tab: window) gets its own isolated environment.

I frequently use this to log into websites with different user accounts for testing purposes.

Good to know, I'll take a look!

To be a little more explicit, I think you need to spawn a private window from a non-private window to get a new environment. If you do it from another private window it uses the same sandbox.

And unlike private browsing windows, they persist across browser restarts until all their tabs are closed.

Not that I've been able to find. Brave would be the obvious candidate to implement this, but the impression I get is that they're not all that interested.