The check-in process was very smooth. If you're not familiar with Rome, we highly recommend using the driver Massimo can arrange from FCO. It was cheaper than a taxi (or Uber) and much more comfortable. The driver will bring you to get your keys and then drop you off at Massimo's apartment. Once we arrived, everything was as described. It's a nice, clean, small apartment (small kitchen and dining area, pullout bed/couch, small bathroom and comfortable shower) in a fantastic location, literally steps from the Trevi Fountain. It felt more "authentic Italian" than a hotel experience and the in-unit AC is a nice touch. We walked everywhere - you can get to most major attractions within a 25 minute walk from Massimo's place.
If you are a light sleeper, you can hear noise at night from activity around the Trevi fountain but it didn't bother us. We had issues connecting to the wifi but plenty of places nearby offered free wifi so it wasn't an issue.
This was our first of many Airbnb experiences but we would gladly recommend Massimo's apartment if you're visiting Roma.