Betterteam offers a simple way of categorizing candidates: click the Like or Reject buttons, or pick one of the many statuses from the Other menu, when viewing a candidate.
Only you can see the status you give a candidate. No notification is sent to them when you click Like or Reject, or when you choose another status from the Other menu.
If you want to add more detailed feedback about the candidate, you can save it as a [candidate note] that only you can see.