The portuguese league has produced many good players (Cristiano, Falcao, Carvalho, Pepe, Di Maria, Ederson , etc) but also many flops (Mangala, Joao Mario, Anderson, Andre Silva, Jackson Martinez, Renato Sanches, Danilo, etc) Its very risky to pay 70 million for a player from an emerging league, its a gamble. The thing is that the market prices have scalated so much that now the gamble is huge.
He looks really exciting, creative, goal scorer and lot of stamina I would gladly have him on the team but he's a gamble we may very well end up regreting loosing him to another club or relieved that we dodged a bullet.