I think Tonali is a good signing for Newcastle as a 23-year-old and future-oriented signing player. I think he will be successful at Newcastle United. There is no doubt that he will be one of the indispensable names of the starter 11 in the future.
AC Milan is like downgrade their squad for letting their good players to leave. They already lost Ibrahimovic, Giroud will retire soon, they only have Hernandez, Leao, Tomori and Calabria, the other are just to complete the squad.
Arsenal sign Declan Rice for 105 Million Euros, while the cost of Newcastle to sign Tonali is only half of it, I think both of them are good players, but Rice is overpriced and overestimate.