This apartment is quite large. There are three bedrooms (and a living room that can double as one), multiple beds, and two bathrooms. For our group, with two families, it was an ideal setting.
If you're there in the heat of the mid-summer, as we were, the blast of cold air from the air conditioning as you open the door was very much welcome. There are A/C units in just about every room. The clothes washer was a nice amenity, though (as is more common in Europe) there is no dryer, but instead a drying rack.
If you're coming from another country, don't forget to bring power adapters with you. There are more than enough outlets, but they are a special three-pronged outlet that is unique to Italy and a few other countries.
We were forewarned about the elevator having a capacity of only 3 people (and a 250kg/550lb weight limit... so if you've got heavy luggage or big guests or a combination of both, be sure to do the math!) but let me just say that this elevator was a blessing. Lugging 50lb suitcases up four flights of stairs isn't something you want to be doing. Focus on the fact that there is an elevator, not that it's smaller than ones you may be accustomed to.
Location-wise, if you're taking the train in and ending up at the Termini station, this property is close enough to that where you can wheel your luggage without too much of a problem. The two closest Metro stations are a 10 minute 1/2 mile walk to Repubblica (the A-line, best for getting to the Vatican or the Spanish Steps) and a 6 minute 1/3 mile walk to Castro Pretorio (the B-line, best for Colosseo which is right by the Colosseum). Multiple restaurants are close by, as is a supermarket, and - most importantly - plenty of gelaterias. We always felt safe in the neighborhood, even at night.
Our host Paulo was very nice, and as others have mentioned, is very helpful when it comes to providing maps and directions to nearby attractions, making restaurant recommendations, etc. We were able to co-ordinate an earlier check-in than the advertised time (a good idea to install WhatsApp on your phone and communicate with Paulo that way), but it's probably worth investigating some of the luggage storage websites out there as there are a few nearby the apartment in case an early check-in can't be accommodated.
This apartment definitely met our needs. Our host Paulo was pleasant and reasonable to deal with and we had a great time during our stay in Rome. Book with confidence!