The 2025 edition in Qatar marks the first since a change to an annual format and the debut of a 48-team tournament, following the end of the previous biennial cycle.
Duff, who enjoyed a trophy-laden career with Chelsea, Fulham, and Blackburn Rovers, serves as a member of the FIFA Technical Study Group, led by Arsenal coaching icon Arsene Wenger.
Ahead of Thursday’s final at the Khalifa International Stadium, the 46-year-old retired winger assessed the Cadet tournament, applauding the technical quality on display and the high standard of competition throughout the event.
"I've been really pleasantly surprised I'd have to say. The minute you hear 16, 17 year olds, you think kids but they're not, they're young men," Duff told Flashscore.com in an exclusive interview.
"There's a lot of beasts, physical beasts in the tournament. So now I'm really impressed and obviously there's been a high technical aspect as well, a lot of strong teams.
"Here, listen, because there's 48 teams, of course there was poorer teams as well, but that's where I think the opportunity is there for these lesser nations to grow, improve and come back stronger next year."
Beyond the remarkable 324 goals in 102 matches, averaging an impressive 3.18 per game, the tournament has also showcased a crop of emerging stars expected to follow in the footsteps of Victor Osimhen, Juan Mata, Phil Foden, and Toni Kroos, all of whom were first noticed on this stage.
When asked about the players who have impressed him most during the competition, Duff commented: "Here, if I'm speaking about the final, it's obviously (Mateus Mide) of Portugal and the top goalscorer of the tournament (Johannes Moser), I think he scored in every game.
"I guess the one standout for me that I really enjoyed watching throughout was Cavan Sullivan with the United States. Unfortunately, he's gone home early so he won't be in the running for many individual awards. Of course, I must say he really excited me also.
"From a collective point of view, I have to say the African teams. I think I watched Zambia who should have beaten Brazil; Morocco, Tunisia and the fans that they brought. They played with just an amazing energy and quality so it was refreshing to see."
The former Shelbourne manager was also asked about the areas in which youth football has improved since the inaugural U17 World Cup, which was hosted by China in 1985, where Nigeria defeated West Germany in the final.
"I have to say, for sure, I just think the game at every age group just gets quicker and quicker every year,” he added.
"So even at senior level, which is when I played 20 years ago, it's just a different level. And also now, obviously 17s World Cup, you expect maybe not a lot of speed or not a lot of physicality, but I was shocked to a point that 17-year-olds they look like young men.
"And as I just said there, the technical aspect as well, it's been very, very high. So I've been so impressed.
Obviously, my first U17 tournament, I was lucky enough to play in two U20 tournaments a long time ago. They were the best days of my life, representing your country with your friends when you're so young. And I think that's also a reason why I've loved it so much, just watching young men play for their country and watching how much it means to them all."
FIFA has decided to hold the U-17 World Cup annually to fast-track the development of young talent and offer more regular competitive opportunities.
The governing body believes a yearly format enables scouts, clubs, and national teams to spot promising players more consistently, while giving youngsters crucial experience on the international stage.
Duff has praised this move, while highlighting its potential to nurture the next generation of football stars.
"I think the more football you play at this age, the better. I used to criticise my players in Ireland when they'd be complaining that they're playing three days later," he said.
"These are the best days of your life. Now they're young kids, seven games to win a tournament, usually. It's eight now, it's an extra game. What's 90 minutes in your life? It's absolutely nothing. As I said, it's been brilliant.
"And you cannot play enough football. So, every year, absolutely, it's brilliant. To make it every two, three, four years, I think would be crazy. So, whoever came up with the idea of playing it here every year, perfect.
"Of course, it's obvious that Europe and South America will always have an ace over the other parts of the world. But for someone who comes from Africa, what do we need to do to see that in the long run this gap is closed, especially at this level?
"I wouldn't get too infatuated with there being two European teams in the final. It could easily have been Brazil, it could easily have been Morocco and it could easily have been Burkina Faso."
The Portugal versus Austria clash marks the first time in 34 years that the U17 World Cup final features two teams making their debut in the championship match. The last occasion two first-time finalists met was in 1991, when Ghana edged Spain 1-0.
Additionally, this will be only the third all-European final in the tournament’s history, following England vs. Spain in 2017 and Germany vs. France in Indonesia two years later.
