I've stayed with David for 3 nights. The room is spacious, clean, and well decorated. There are only two easily reachable power outlets and not all European plugs fit, so keep this in mind if you travel with a lot of devices that need charging.
The location is great except for one thing: there is a pub right across the street and the room is on the 2nd floor. Which means up to around midnight you get to hear passionate drunken conversations whether you like it or not.
On the upside it takes a maybe 20 minute walk to piazza del Duomo, Castello Sforzesco, Sempione park (this one is highly recommended) and there is a lot of restaurants of all kinds in the area.
This apartment has something that I don't frequently come by with AirBnB: a really fast Internet connection. Need to download a season of your favorite show on Netflix to binge watch offline? It took only a few minutes for me. Two thumbs up.
David is a very nice and easy going person. He's very busy running his businesses so we didn't interact much but when I needed help or advice, he did his best.
Next time I'm in Milan I'd definitely consider staying with David again (this time with a pair of ear plugs, perhaps).