Yes, for those user login after admin posted that boardcast on the site, they will still receive this pop up notification, you can watch my video here :
http://take.ms/niURp
Once this pop up appear after user logged on the site, it will never appear this pop up for the next time.
Since you only show `Me & Friends` filter on the dashboard, other user who not friend with the admin, other user unable to see the stream under this `Me & Friends` filter.
If you select notification before you post boardcast on the site, it will send this notification to the user, so the user can able to click on that system notification link (
http://take.ms/vQR5x) then it will redirect user to access this broadcast stream on the page.