We stayed here for a week to finish up our most recent trip to Italy, and absolutely fell in love with the place. It's even better than described, with the location being ideal and the views exceptional. We are already planning our return next year!
I'd assume if you are looking, you know about Trastevere, but just in case, it's a fascinating neighbourhood across the river from the historical centre of the city. Assuming you're moderately fit, walking almost everywhere is an option (though we did do a taxi to the Borghese Gallery and walked back), with most of the sights being within 20 minutes. It's obvious that tourism has affected the area somewhat (which I suppose is inevitable when it has so much to offer) but unlike many other areas within the old city, there is still very much a vibrant community of locals. This makes staying here a real treat, and gives some small taste of the true Roman lifestyle which can be so hard to find closer to the Campo de' Fiori/Piazza Navona/Pantheon areas.
The apartment is very warm and welcoming, and a fantastic place to put your feet up after long days of sightseeing. We felt very much at home there, and it was a true joy to be able to sit with a coffee in the morning and watch the square come to life with locals getting started with their day. In the evening, the crowd is much more diverse, but no less interesting to have a birds-eye view on. Naturally, being a social centre, there is some noise from the square at night, but as the bedroom is set back at the opposite end of the apartment, it didn't affect our sleep at all.
The host is extremely professional, giving lots of information about the area and tips to best enjoy the neighbourhood. We had no issues while we stayed, but my impression was that if there were, she would address them immediately.