Personally, I don't see how spending 50M on a 28 year old who won't be good enough for anything but Lingard duty once his pace goes makes sense when we have 2 potentially world-class left wingers who badly need games at LW.
Now that we've bought Lukaku, who is young and rarely gets injured and have Mourinho as our manager, and he basically never starts with 2 up, Rashford is going to either be a backup here or he'll have to learn how to be a winger or a 10. Same for Martial. And while Rashford is quite smart for a young player and did play wide when younger, he still badly needs games to learn, like any 19 year old. And Martial is basically converting positions and is pretty clearly very raw in terms of movement as a winger. And of course both need to learn how to defend like any young wing forwards do.
So, sure, Perisic would very likely help us this year giving us width, crossing and defensive work on the left or right, especially in bigger games, but I don't think he's any better than Mata in games against weaker teams, Mkhitaryan can provide some pace on the counter out right too and the young guys need games.
Much rather see us use that sort of cash in a different way, like signing a proper LB who can run and defend in case Shaw gets hurt, or whoever we think is the best 16-17 year old on the planet like Madrid just did with Vinicius, or just keep it around and throw it at Griezmann, Bale, Sanchez, Verratti or another actual star next summer.