Seems counterintuitive to me that
Last_Name = $User.Profile.Last_Name
But
FirstName = $User.Profile.First_Name
DisplayName = $User.Profile.Display_Name
RealName = $User.Profile.Real_Name
Despite all the profile.atrribes being underscores all PSCustomObject attributes except Last_Name have no underscore.
Either they all should have an underscore or all shouldn't.