This has potential to be a legendary freebie or a spectacular failure and its up in the air which way it goes.
There's no doubt the guy has the talent to play here, if he was 21 I'd trust Pep to mould him into what he wants in time if Pep believes he can do that. At 29 with most of his career spent waltzing around doing what he wants when he can be arsed, there's serious questions as to whether he can change now. The one thing going for him in that regard is he's currently seen as a failure at united and took a lot of flack, if he finds that determination to prove them all wrong under Pep it could be frightening.
There's a lot of questions about his work rate and rightly so, I'm questioning it too but there's loads that want to see Grealish in the middle and he doesn't even work as hard as Pogba. I can't see how he could play as a 6 even as a backup, an 8 is more workable but him or gundogan as the 6 options to cover Rodri isn't good and there wouldn't be room for him and an actual dinho replacement without us getting rid of somebody on top of mendy and dinho this summer.
Easy to say on a free it's worth a risk but if he's toxic that's going to upset the squad, him coming in means nobody else and if he doesn't work we're left short in midfield again. It's a bigger risk than it seems but if it's one Pep wants to take I'm on board. Added bonus is united fans will be fucking livid.