Given that 'blunt' means 'not smart' and that 'mettle' means 'wit; intelligence', I believe that the statement that best paraphrases "What a blunt fellow is this grown to be! He was quick mettle when he went to school" is "This man, who was smart in school, has grown up to be unintelligent".
Benefits could include: locating a hostage, lowering crime rates, population stats
disadvantages could include: invasion of privacy, violation of our human rights
hope this helps you ! -isabel
