Ekaterina's apartment is in the heart of testaccio. You aren't in the craze of the historical center nor that of Trastevere. You can walk to Trastevere though, it's 5-10 mn by feet. The apartment is calm, and the beds are extremely comfortable. It is a very functional apartment. Some caveats if you plan on having a couple of meals at home: No microwave, no dishwasher. And very little daylight comes through the apartment.
Other than that, it is very easy and in the heart of it all.