Dani..I like the defense drive of this dog! the owner is so lucky to have this kind of dog. Like father like son!
Ron
The defense drives are there which is always good to see, i personally would not do too much of this type of training with a young dog..
The "stranger behaving suspicious" type of 'test' should be very brief, especially in the case of Grief where he shows very good level of suspicion for he's age.
And no real need to do this too often,if less of this 'test' is done he can become more serious in good time at maturity IMO.
Yes I agree, this will be (and already is) a very good dog! And when I say "good", you know what I mean 
Very well could be like the Sire in the near future..!