I'm definitely in the "Give Duffy a go camp" myself.
I actually caught most of the Peel game on Saturday (first time in months) and Duffy really impressed me with his improvement - moved well, kicked true, milked a free that turned into a goal - he was lively.
Rather than have Duffy behind Ballaz as the second option though, I would have him behind Crozier. Early this season Max had the goal-kicking yips and his radar was a little off (lots of shots on goal, but they resulted in lots of behinds, choosing the wrong option and reading the play too slowly) IIRC... but at the same time he was also consistently racking up solid-enough possession numbers on a HFF / midfield rotation.
Now skip forward a few weeks - he's kicked four goals in both of his last two peel games IIRC and he looked downright dangerous to me in his last game. He matches Croz for size and speed and both those guys present a scoring option... but Croz has always been the far better tackler overall and this consistently puts him ahead of Duffy.
Croz has been a tad underwhelming in possessions, scoring and tackling in his last couple of games - Duffy however has been pretty solid in two of those three at least down at Peel. I say keep Ballaz and Sonny in the team up forward, but exchange Duffy for Croz against Brisbane and see if anything develops.