It just says Klaassen is on his way from Ajax to Everton.
Will he be doing good in the PL? "He will have to invest hard in his physical qualities but he has the mentality to do it". It's just an article about people giving their opinion about how he'll be doing in the PL.
E.g: Ronald De Boer: "It's important that he chooses a club that really fits him. "He doesn't have the extreme qualities that enable you to do well everywhere. He can't just dribble a few players. He's all round and flourishes in the Ajax tactic (the tactic that Ajax played during the past season), where a striker doesn't only think about himself and players like Klaassen can benefit. He's a team-player.