A dominant display from Championship Derby County was too much for the Brewers to handle as the final pre-season game grinded to a 3-1 defeat.
After scoring a last minute consolation goal against Leicester City just under a week ago, Duffy said Saturday's test against Derby County was the toughest yet.
"Derby were a really good team." Duffy said.
"They will be challenging to go up to the Premier League.
"They shown that they can move the ball really well so it was a different game to what we have this pre-season.
"It was a good learning curve for us and thank God it wasn't in the league for points."
A lot of things have changed since Hasselabink took the reins back in November 2014, personnel and tactics. The former Scunthopre man, Mark Duffy, said Jimmy Floyd Hasselbaink is trying to play the quick passing and attracting game to League 1 this season.
"We are trying to play the quick passing game.
"We came up against a top class team and you can see from the substitutions what kind of quality they have."
Keep a lookout on burtonalbionfc.co.uk for more Mark Duffy quotes in the coming week.