I'm sorry, but this is analysis is quite superficial and something that anyone can conjure up. It uses stats without offering much context to them, and it compares him to a stylistically different defender playing in a stylistically different team.
For context, Milenkovic plays in a back 3. German Pezzella plays as a covering defender, whilst Milenkovic and the LCB play as stoppers. Fiorentina like to keep their back 3 in line and have them drop quite deep, mainly into the box. As the RCB, Milenkovic goes out to the flanks to support his wing back and look to win the ball. He gets into lots of 1-on-1 battles with the opposition ball holder on the right flank, and he tends to throw his foot in quite often. When the ball's on Fiorentina's right flank but not close to Milenkovic, Milenkovic himself tends to ball-watch and lose sight of runners. That's fine in Fiorentina as he expects Pezzella to deal with that whilst Pulgar and Amrabat plug the midfield gaps. With United, however, he'll have to take charge of passes behind him as well, something which I don't see him do often at Fiorentina unless he's dealing with a pass out to the flank.
When he has to deal with crosses from the near side, he always goes towards the near post and tends to do a decent job of dealing with them. However, he rarely if ever, stops cutbacks towards the penalty spot, and he rarely, if ever, positions himself to stop them. Once again, that's a consequence of how Fiorentina play, but it goes to show you what he tends to deal with. He's very good at defending the far post, but when he gets sucked into the middle, he tends to lose awareness of what goes on behind him. Once again, Fiorentina's setup, but there you go.
On the ball, he's still a safe player and doesn't tend to go forward with the ball so much. Fiorentina tend to use Castrovilli to drift out wide to support the wing back, and Milenkovic tends to stay back with the rest of the back 3 to cover the right side. Don't expect him to go on marauding runs with United or play raking long passes often.
Overall, I think he's getting a bit overhyped due to the United links. The fact that he's quick despite being quite tall means that he can overcome most of his weaknesses, and his ability on the ball is another tool in his locker. However, don't expect him to be flawless. Do, however, expect him to be aggressive and strong on the tackle. He'll go in early, and he won't pull back on his challenges.