The apartment is spacious, clean and well-located, although from the Coliseum (besides the monument itself, the closest subway station is located nearby) it is quite steep uphill way. Through the parc it's ok, but in the evenings it's closed and you will have to count around 15 mins to go around the parc and upstairs some three steep flights of stairs to get to Mecenate street where the flat is located.
Communication with the owner leaves a lot of room for improvement, to say the least. I advise to immediately buy an Italian sim-card upon arrival in Rome from abroad, as the owner will expect you to communicate with him upon arrival to the city centre in order to arrange the delivery of the keys and signature of papers. Also, don't count on any flexibility regarding check-out times (I assume also for check-in), regardless of the duration of your stay.
Finally, the apartment is not heated. I understood from the owner, who apologized for that, that the apartment is only available from May until I suppose end of the summer, when he expects temperatures to be high enough for this not being a problem. Rome however can be cold at night, also in late spring-summer, and was indeed while I was there. That made the stay somewhat uncomfortable.
Finally, the flat is in my opinion also overpriced, so I assume anyone would only chose it if other flats with better price-quality ration are taken, as was my case (last minute decision to travel, already start of the peak season and long stay).