You're correct - once you're logged in, you'll see a little number (indicating how many Players are logged in) on top of the "Account" icon on the lower left side of the AGS navigation menu. Selecting that icon will also show who is logged in (with a $ icon to denote who is the primary account and any purchases would save to that account) and allow more Players to log in.
To answer your question, the "Account Linking" is a settings for cases where 1 admin "account" could manage multiple machines. Since this is more of a Commercial use case, and since it was confusing a lot of users, we decided to remove this from the AGS Settings for now!
