The apartment is ideally located, very clean and spacious for 4, could just be a bit noisy at night. It is in a lovely pedestrian street where we also found 2 great places to eat + an excellent sandwich bar. Campo dei Fiori is 2 min walk, great atmosphere in the evenings and nice market every morning. We never used public transport since you can walk to most historical sites from the apartment.
Federico was very helpful by phone and email, we did not actually meet him but one of his friends met us at the place and was very helpful friendly and helpful.