We loved our stay at Marco's apartment!
First, the street it is on was magical -- no cars, and instead, tables set out from various restaurants, with attractive lighting at night. We felt like we were in a romantic movie from the 1950s. We had very good meals at different restaurants, and sat out at others for our coffee and cornettos in the morning. Things were never very noisy, and at night things were very quiet.
Marco himself was super nice and helpful; it felt like we made a friend. (We also met his mom, who was really sweet.) Marco is a furniture maker, and he has a shop a block away. Because we arrived before check-in time, we left our bags with him at the shop and went exploring. When we returned, he had already transferred the bags to the apartment for us. He walked us over to the apartment, showed us around, and gave us the keys. Same thing on the day we left -- we left the bags at his shop early and went out, coming back to pick them up before taking a cab to the bus station.
The apartment is up three flights of stairs, but they are well-lit and easy to negotiate. The apartment was just as depicted and very clean, had a comfortable bed and great pillows, and had elegant and eclectic design touches. It also felt very secure and had great locks. The kitchen was well-equipped. The wifi was fine, and the air conditioning worked well (although we did not really need it).
It is an easy walk to the Vatican -- less than 15 minutes to the museum entrance, and less than that to St. Peter's. In fact, you can see the Vatican wall at the end of the street, about 3 blocks from the apartment. We also walked to and from the Trastevere neighborhood, which was about 22 minutes. The walk to the Trevi Fountain and Spanish steps was about 25 minutes, and the Coliseum about 40 minutes walk. We also took taxis from time to time, and there is a stand less than 5 minutes walk from the apartment.
In short, we would love to return to the "Borgo" and stay at Marco's place!