We had a really great time staying in this apartment for a few days. It's really well situated for exploring the city as it's walking distance to most of the main sights and there are lots of nice squares and cafes/restaurants nearby.
The apartment was very clean and ideal for 2 of us, although I imagine it would have been comfortable for 4 as well. Antonio met us even though we arrived late at night and shared a useful list of recommendations.
The only aspect that didn't work for us was the noise coming from the nearby Campo de Fiori each evening when the bars closed, and each morning when the market is being set up. However, if you take ear plugs it should be fine!