He would add a lot of dynamism to the poor summer. I had this a 5/10 window before a whistle was blown and I think the manager is going to have to undo, this new system and revert to a double pivot midfield. In such circumstances (though I don't like Bruno wide) it's permissable to have Onana / Casemiro as the double with Case stepping forward in possession, Mount as the 10 and Bruno out wide on the right.
I know the manager has mentioned transition but you need clinical players to capitalize which United don't have so I think being a team that ushers control of possession is more beneficial in the long run.