The flat is fantastic. Located only a few walking minutes from great restaurants, cafés and boutiques, it is a great base in Trastevere. Walk only a few minutes more and you cross the bridge over the Tiber to reach the center and all the sites. And still, it is super quiet, so you can sleep without earplugs.
The flat is cosy and well decorated. Most decoration is French- but heck - it feels local.
I give 4 stars because the communication with the host was sub optimal. However, looking at the reviews from previous guests, we must be the exception. It took us some sweat and effort to be able to drop our baggage in the apartment and get the keys. If that had been better, I would have given 5 stars.