For everyone comparing Barella with Vidal and Nainggolan, this is my explaination.
Barella can do assist from the right side, and link up with our RWB like Hakimi, plus he going forward with ball, but not shoot often like Nainggolan.
Vidal in my opinion do more defensive duty than Nainggolan or Barella, because Pirlo and Pogba.
Barella most likely an unique type midfielder, no one like him, he is special because his small stature, plus good playmaking ability.
Vidal is Vidal, Nainggolan is Nainggolan, Barella is Barella. They are world class in their peak.