Cristian's place was well-situated for our purposes: walking distance from both the Rome Termini station and the Colosseum. It was also a five-minute walk from a grocery store, which was handy for us. It's at the end of a street, so there's not a lot of traffic, plus there was an abundance of graffiti (we noticed it everywhere in Rome), so I felt a bit apprehensive when we first arrived about the safety of coming and going during evening hours. Cristian assured us that we need not take any special precautions, and we did feel at ease our whole stay, evening comings and goings included.
Cristian was prompt with communications and a pleasant host who made homemade chocolate chip muffins for our arrival. :)
Two notes: (1) the bathroom shower was a tight fit for my 5' 11" husband, so don't plan to be able to wash your feet without contorting yourself if you're on the taller side; (2) there's a motorcycle repair shop on the other end of the street - this was not an issue for us because (a) we used the AC often, and (b) we didn't mind the occasional revving-motor sounds.