Kovacic, an attacking midfield player that Inter are attempting to convert into a regista with varying levels of success. A good player? Yes. What United need? Not a chance. He's still quite poor defensively, and definitely lacks the positional awareness to play in United's midfield pair.
You've also mentioned Herrera. He's another one who's an attacking midfielder, and he's playing well, but unlike Kovacic he isn't being played deep even slightly. You haven't stopped tracking him - Cooke was at Bilbao's game with Almeria last month - but his release clause is ?30 million, and Bilbao have said they won't accept anything less. So ?30 million for another player to compete with Rooney and Mata and Januzaj AND Kagawa in an AM slot. Mhmm.