Montgomery took charge of Hibernian earlier this month after Lee Johnson was shown the door following a poor start to the season.
He has had a positive impact on results and Hibernian beat St. Mirren 4-2 at home on Wednesday night to book a place in the semi-final of the Scottish League Cup.
Duffy conceded that the complaints around Hibernian earlier in the season were that the team had no identity and believes Montgomery has definitely changed that over the last couple of weeks.
He insisted that there is now a definite style of play and the new Hibs boss has also managed to create a sense of positivity around the club by building a connection with the fans as well.
Duffy said on BBC Radio Scotland: “You can see he is already making an impact on the team and the style of play.
“I have heard various other people say that they didn’t see an identity of the Hibs team but you can see that now.
“He is also building a real rapport with the fans.
“At the end of the game he went over to the Hibs fans and you can see the atmosphere changing and there is positivity about Hibernian just now.”
Hibernian will take on Aberdeen in the semi-final of the Scottish League Cup in November.
