Just tried it out - definitely an improvement UX-wise, but it still essentially runs two copies of Firefox rather than only isolating profile-specific features.
>This feature is separate from the about:profiles experience, and we currently have no plans to change how about:profiles works. You may continue to use about:profiles if that is better for your workflow.
If you don't see it in the main menu yet, type `about:config` into the address bar and toggle `browser.profiles.enabled`.