I think he will play as one of the two if Benitez uses a 4231 formation.
He'll take the ball on the turn from defence and drive forwards using his pace...or pass the ball around proactively...while not being a killer playmaker like James he will look to cut out opposition midfielders through passing between them or knocking the ball past them and leaving them for dead.
Potentially looks good but i doubt he'll be lighting up the league from day one. Im not sure if he will do well in the league and seemed a season away from a real breakthrough as hes not a starter for sporting yet and will be 23 this month.
My guess is that hes a rotation player and will compete with Gbamin, Davies, Onyango Allan and Doucoure.
He does offer two things which they dont, passing and pace. If he comes good then he could be very good as hes someone who would be hard to press in the middle of the pitch and looks dynamic...i doubt he would be caught on the ball like Davies.
Im a bit negative on him as it seems like a risk because hes not a starter for Sporting at 23 but if he can step up another couple of levels then potentially hes a very good player.
The money doesnt seem huge at €18mil / £15mil but the pressure will be on him because were crying out for a player like him...whether hes good enough, time will tell.