Stayed at the apartment for three nights. Had some initial hiccups with the check-in but once you enter the apartment, open the window to the street you will forget all. The location is marvellous: hardly 50m away from Trevi (which we ended up visiting every night) and mostly less that 750m from main locations like Pantheon, the Spanish steps or the Piazza Venezia : Centre of the centre.
Considering its such a prime location, you have walking people, laughing crowds and music till midnight. One can complain about the noise, but it added to our Rome experience.
The apartment is housed in an old building so the steps are a little uneven but once aware of it, it should not be a problem.
One thing is for sure you wont be disappointed.