Getting the keys involves going to an office near milano centrale which is the train station on the other side of the city from where the apartment is located. It’s convenient if you get to milano by train. If you aren’t and want to get the keys directly at the apartment you have to pay an extra (small) fee.
Apart from that minor inconvenience I would say that the apartment is as advertised. Clean and in a good area. We were 5 people and had no problems with space. If by the time you are booking metro line 4 is complete this is an added bonus of the apartment - otherwise metro line 2&3 are only about a 10 minute walk.