Pros: This place is huge, and the location is exceptional: in the heart of the historic center, 15 minutes walk from St. Peter's Basilica, 10 minutes from the Pantheon. The area felt very safe, even at night, and it was surprisingly quiet. The apartment was very warm: the building is old, but the heating does its job perfectly.
Cons: during check-in we did not know which floor to go to, so we ended up knocking on random doors, since our phones did not work yet. This what somewhat awkward. Once we found the right door, everything went great and the hosts were very friendly. The wi-fi was flaky, and virtually did not work in the main bedroom. The stairs leading to the apartment are narrow, steep and curvy: this was not a big deal for us, but may matter to some people. The main bedroom has very little natural light, but the electric light was more than adequate.
Overall: very positive experience, will rent it again if given a chance (but will make sure I know which floor to go to, so I don't have to knock on people's doors again).