At the yesterday's conference I felt that he is really torn up about accepting the move to Man Utd... Maybe it's just about being difficult and emotional to leave Sporting, his project and fans... Or maybe he really hasn't decided if he should move. Of course, it might be just because he's in negotiations, and you don't talk like it's a done deal before that.
Personally, I think he could be successful in Man Utd, but he will find a club and player culture that will take time and patience to change, and I don't know if that will be really given to him. Specially being a young manager with no curriculum in the big leagues. One thing is sure: he and his team are really professional, they prepare every aspect of the game: players physical and mental well being, a strong group mentality, the study of the adversaries and teaching each player what's his role, bringing out the best of each player, etc. It's not about Amorim only, but his highly professional team.
He complains a bit about having matches every 3 days, how that limits the tactical work and it's more about recovering the players for the next match. The good thing about Sporting now is that the players have been together for some time, they know their roles and what he expects from each of them. New players can integrate better when everyone else knows their role and the team's dynamics. Amorim will have to start from scratch and that will take time and probably some bad results at the beginning. I'm just doubtful that he will have the support he had in Sporting, from the bosses and from the fans.
He joined Sporting in March 2020, so much later than now and with the club in shambles. Got 5 victories, 3 draws and 2 defeats (the defeats with the other two big clubs of the portuguese league). Next season, his first full one with pre-season and everything, ended up by winning a title that eluded Sporting for 19 years.