Best of luck to him to be honest, it's a good move for him. Better defender than given credit for and very often scapegoated for the whole team's deficiencies.
Hopefully his minutes will go to Tuanzebe instead of RoJones.
I really like Chris Mike Smalling as a character. He is also a very good player, and if you’re looking for a msotly defending defender, and have another CB with some leader skills already, he is one of the best options around.
For managers like Southgate, Guardiola, Solskjær, he solves some problems and introduces others. Some say he is still a good backup option, but I disagree: If you play out from the back and want ability to control the ball and play off high pressing, you need two CB’s comfortable with the ball and with passing through tight areas. Not necessarily geniouses, but comfortable enough. If one of them are injured, and you introduce Smalling, it’s not merely a matter of plusses outweighing minuses - you have to change the way you play, affecting all other 10 players.
For Mourinho, he is perfect apart from one thing: Mou always needed a warrior-leader in defense. Smallings best games were maybe with under Van Gaal with Blind, the only CB we’ve had the last five years with much leadership qualities. Unfortunately, he was not warrior enough for Mou’s football, and so we had no one like Terry, Ramos or Materazzi beside Smalling. Ironically, under Mou, Smalling could have been a really good foil for Maguire, but Mou weren’t afforded him, and under Solskjær, his ball playing skills are just a bit too detrimental.
I love the Mike who is almost never passed, or always onto a header. I like more though, that Solskjær want’s to play another way, and that he is uncompromising enough to put maybe the best defensive CB and a very likeable chap, out of the club because he wants us to play football a certain way.