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GitHub User: norman
It's actually new in version 4.0, previously it was enabled by default.
No, only Active Record.
If you don't use slugs, then yes. This is precisely the "user name or email" example that you mention. Otherwise if you use slugs, you can use a value that's not necessarily unique like a title or name, and FriendlyId will automatically append numbers at the end of the slug when necessary to keep it unique.