Massimo's apartment is brilliantly located. The pantheon is 5 minutes walk and it's about 25 minutes to the Colosseum & Forum. The Vatican City is close too ~10 minutes.
There were five of us in our group, plenty of space for sleeping and lounging around. The kitchen was well stocked although we only used it to serve drinks. One thing that we hadn't spotted from the ad is that there's only one bedroom. There's a sofa bed in the lounge, twin beds in a room by the kitchen and then a double in the bedroom. It was absolutely fine for us and we loved the social aspect to the apartment. Might not be the place for you if personal space is important.
We were here in Feb and it was really cold outside, the apartment was lovely and warm. Definitely worth mentioning that the beds were really comfy, everyone slept well.
Massimo was great on the communication front, offering to arrange transfers etc etc. Really helpful. I need to come back to Rome to finish my sightseeing, I'd actively choose to stay here again.