The other reviews are accurate and reflect how helpful Domenico is.
The apartment is a stand-alone self sufficient space located within a registered hostel. Italy has a requirement that all registered accommodation collect passport ID from guests so don't be surprised if you are asked for ID.
The apartment is right in the middle of a very hip student district full of awesome bars and cafes. The walk from Roma Termini is a good 20 minutes - further than it looks on the map! But the apartment has several trams around the corner that go straight to the Termini every few minutes.
A very convenient place for great value. The only downside is that it is right above a bar which may be a little loud at night for some. The windows are soundproofed and it wasn't a problem for us.
Grazie Domenico!