"I'm just happy that we've done the business for Cousin and delighted that he'll be able to do the job for us that Campbell was going to do if he signed," Duffen told the Hull Daily Mail.
"Where he'll play is up to the manager. He makes all decisions regarding positions."
Duffen continued: "Cousin has ability and at 31 he has the experience as well and that's an added bonus.
"He scored in the Old Firm clash for Rangers and matches don't come any bigger than that.
"I'm delighted with the way the transfer window has gone. It has enhanced our squad and we've a nice balance now."