Prime location, literally. The apartment is super close to public transportation - tram, subway, and Milano Centrale. Even with all our luggage, my sister and I walked to and from the Milano Centrale station - it takes about 10 minutes, which seems long if you think about it, but when actually walking, not long at all.
The place is steps away from Porto Nuovo, where all the restaurant/bars/Eataly/cute shops are, and it's also walking distance to the Brera district. You could take a train to the Duomo, but my sister and I walked everywhere and it was totally fine.
The place itself is cute and super safe. He has a full length mirror, which is always a plus in my book and the wifi is fast. As for water, Leo has a Brita filter which saved our lives. There is a 24 hour supermarket about 5-7 minutes from the place, so if you need anything, that's the place to go. It was a little scary when we first arrived on a Saturday because everything was closed and the streets were dead at night. We realized that that particular street and area has a lot of corporate office buildings and is pretty dead on the weekends. When Monday rolled around, the streets were packed with the hustle and bustle of everyone going to work and going about their days.
Definitely do your research before going to Milan, which will help out a ton. Leo communicates well and responds quickly, but we didn't get a chance to meet him. Checking-in and checking-out was easy, but friend who greeted us didn't speak much English and pretty much just showed us the apartment and gave us the keys, but that was fine. There were several mosquitos that got in, not sure how because we never opened the windows, but other than that, I would say that Leo's place was awesome!