Marco's place is in an excellent location. It's about a 10-15 minute walk from Rome's Termini train station. It is about a 8-10 minute walk to the nearest Metro station Manzoni), which gives you access to public transportation for Rome. It is located way inside, passing through a courtyard. It is very peaceful and private.
Marco is an exemplary host. He met us and helped us check-in, showed us how things work in the apartment. He gave us a bottle of wine as welcome gift, explained how the public transportation work in Rome (e.g., where to buy tickets), recommended attractions (e.g., including those that are 'free' to access), restaurants, etc., using the maps he has put in the apartment for later reference.
I'm thankful to Marco. I lost the keys to the apartment on check out day. Even though he was away from Rome, he immediately arranged to have someone make replacement keys for us. Otherwise, we wouldn't be able to re-enter the apartment and definitely would miss our flights.