I had a good experience staying at Giancarlo’s flat. The main selling point is the location… from there you can be almost anywhere in Rome within 30 minutes, either on foot or by taking one of the numerous buses that serve the Piazza Navona area. There are many restaurants, bars and shops in the immediate vicinity. Also, Giancarlo was friendly and very responsive to any concerns.
The flat is a loft studio with the bedroom area on top and the living room, kitchen and bath beneath. The bedroom area is reached by a rather steep spiral metal staircase, so if you have any mobility concerns (or have to pee frequently at night) this is probably not a good solution for you.
The street where the flat is located is small and quiet compared to some other streets in the immediate area, but the flat can be noisy — either due to passers by on the street below or due to neighboring apartments (the building is old and not well soundproofed).
Pro tip: be sure to point the remote control very directly toward the air conditioning unit so the signal has the desired effect. It took me days to figure this out.