score:0
Rhoads, Dewey and Michie say, in Mark as Story, page 83 (third ed), the demons in Mark's Gospel seek 'to get power over Jesus by naming him as "the holy one of God" and "son of the most high God." These statement might be true, but we can see from that analysis that the were not intended to be "good".
Rhoads, Dewey and Michie (ibid, page 61) say the composer of Mark uses "considerable storytelling skills". I see one example of those skills to be his ability to present to his first-century audience the portrayal of Jesus as son of God in such a way that early Christians could not be accused by Jews of blasphemy or by the Romans of mocking the emperor, who was regarded as the son of a god. In Mark's Gospel, only outsiders call Jesus the son of God.
So, when the demons refer to Jesus as "the holy one of God" and "son of the most high God", the Christians could not be faulted, because clearly the demons were opposed to Jesus. Even when Jesus does not allow the demons to speak "because they knew who he was", Mark's audience knew this was further, unspoken evidence that Jesus is truly the Son of God. When the High Priest raises this topic by asking (Mark 14:61), "Art thou the Son of the Blessed?" the Christians remain blameless. The centurion watching the crucifixion says, "Truly this man was the Son of God," a sign of approval from a Roman of some importance. God himself describes Jesus as his beloved son (Mark 1:11; 9:7), and God is above criticism.
Testimony from demons is powerful, because they knew the truth about Jesus, even if they were the embodiment of first-century evil. Mark's author has made good use of their testimony to ensure that Jesus was properly recognised as the holy one of God, the Son of God. The later gospels were less constrained, so we begin to see Jesus directly referred to as the Son of God.