We spent 4 nights at the apartment, and have enjoyed every minute of it. It looks exactly like in the pictures and, although not too big, has everything we could imagine: A lovely and equipped kitchen, comfortable bedroom and a nice living room facing Largo Library.
As for the noise, the street had the most fascinating sounds. Street musicians on Sunday and pupils waiting to go to school in the mornings. It certainly wasn't noise and when the double glassed window was closed most of the sounds were gone and anyway, at night the street was relatively silent so we could have a most relaxing sleep without any ear plugs.
Luca, our host, was kind and polite. He had done everything to make us feel at home and would help us with any request we had.
The stairs to the 3rd floor apartment are quite tiring to climb however it didn't come as a surprise to us as it was clearly explained in the site and anyway, we didn't expect an elevator in such an old house (we really have seen it in a 16th century Rome map in one of the museums we have visited).
The apartment is really at the center of many of Rome's sites and as such was an excellent base for our tours. The neighborhood is fun to walk in even at night and is safe for tourists.
We had the most enjoyable time in Rome and this apartment was a big part of it.