My boyfriend and I stayed at "Il Nido" for two weeks. The location was absolutely perfect: a minute's walk from Piazza Navona and a two minute walk from the Pantheon (and the city's best gelateria, Giolitti). It's in a lovely old building and the air-conditioning was excellent, an essential for a stay in Rome in the height of summer!
Luigi was very helpful in providing us with plenty of information about the apartment and surrounding area, and while he did warn us that the apartment was small - really small! - it was still a shock. "In my opinion, "Il Nido" is better suited to one person than two, especially for an extended stay.