I cannot say enough good things about this location. Trastevere is ABSOLUTELY the best place to stay in Rome, because you can't walk more than 20 feet without stumbling over a delightful restaurant or bar. The apartment itself is spacious, well air-conditioned, and shockingly quiet given the area. I hear more traffic/people noise in my suburban California home than I did in this "party-district" of Rome. The beds were comfortable, and check-in was easy.
A quick note about transportation, because the apartment is a bit further from the tourist center of Rome: Taxis have a hard time getting to the apartment front-door because of the small, pedestrian-friendly streets, but we learned quickly that telling drivers to drop us off at "Ponte Sisto, Trastevere" got us within a 2-minute walk of the apartment. Taxis are very cheap in Rome, so definitely consider them as an option. We were nervous because we are a party of 5 people and were worried we'd have to get multiple cabs... but there are a surprising number of larger taxis (5-8 passengers) in Rome, without a significant increase in fee. For our larger group, taxis were cheaper than buses or metro for most trips.