The location is great. Giulia's place is very close to the entrance to the Vatican and to Saint Peter's Cathedral. There are also good restaurants and a great ice cream shop around the corner (Hedera is the ice cream shop). There are basic cooking ingredients (salt, oil, sugar, etc) and plenty of pots, pans, and utensils in the apartment.
The apartment is fairly quiet -- it is on the second floor and thus pretty removed from the street. We really liked the patio. We had dinner out there a few times. Once the sun starts to go down, you get really nice light.
Giulia was really responsive. She responded to my questions immediately, and even organized our airport transport at 10pm the night before we left. Federico is a really good driver. There were four of us with carry-on bags, and we fit comfortably in the car.
The house is as pictured on Airbnb, as were the fees (remember that you have to pay extra for linens and that there is a nightly tourist tax).
There were four of us, so one couple slept on the foldout in the living room. This room gets a lot of sunlight early, and the blinds do not block it very effectively. If you plan to use the foldout couch and light bothers you, you may want to look for a place with darker blinds.
Overall, we were pleased with our stay and found Giulia and Federico to be very welcoming and accommodating.