Not sure if there's slight confusion here. If you have FD's on and select TRK/FPA you end up with the "Flight Path Vector Director!" If flying manually this can actually be quite difficult to follow so is best used with AP. This is typically what you will see when doing a Selected/Selected NPA.
Bottom line - the Bird should be used as much as possible in non-normal circumstances if the FD's are not available. Only exception is when altimetry is affected due pitot /static damage (Birdstrike?)
Regards
A4