We stayed at Navona Square apartment for 5 days over new years, it was an excellent experience. Host was extremely helpful and quick to respond to all of our questions and demands.
Apartment was as described very clean and warm (heating worked well) and we felt really comfortable with specious kitchen, living area, and very nice bedrooms.
Apartment location is amazing!! Its walking distance from main area of the city for both night life and historical sight seeing.
I recommend the Navona apartment and Francesco as a host and hopefully we will have another opportunity to stay at one of his a locationd (Sicily maybe :)