Marco was great to deal with and very accommodating (for example, we needed both an early check in and late check out and had one issue where the hot water stopped working and he was there in 2 minutes to help). He gives you some great recommendations for restaurants and markets as well, and maps and guidebooks are available for your use.
The location is nice, in terms of being super close to both metro lines, a quick jaunt to Termini station and in between the Colosseum area and the other tourist sites, while tucked in a side street. Be aware, however, this is Rome so bring your ear plugs as there is a bit of city noise most of the time. Right on the street, you can find a bakery and some quick food stops along with trattorias and an Irish Pub, which is quite convenient if you'd like a nightcap as it is directly across the street.
The apartment itself is very spacious. It would be way more than one couple would need, good for two couples or a family especially if you wanted to cook in the apartment or spend time relaxing there between sightseeing. We were out and about so much we probably didn't need all that space, but you'll find plenty of room to spread out. The layout is pretty separated so it allows everyone their own space, not often true in European apartments. One bedroom is on the far side of the living room (facing the front street), with use of a bathroom at the far end of the hallway by the kitchen. The other bedroom is across from the entrance with en suite bathroom. The living room is large with a (pull out, I believe?) couch and chairs.
Very clean (you also get a cleaning after 3 days, which I have found is not usually the case in rental apartments, so it was nice this was provided for change of towels, freshen things up) and nicely furnished. Cute theme of the Mok, with lots of related decor.
Just to make sure you know the details (all laid out in the listing exactly as stated): No washing machine, no freezer (typically fine for vacation anyway) and pretty small showers...nothing unusual for Europe. Up one flight of stairs with no elevator.
Marco manages other apartments and a B&B in the building (and their office is downstairs) so it is also nice having such ease of access for any needs you might have.