Hi! My friend and I stayed at Carla's for 5 nights in March and overall it was a very positive experience.
First of all if you are worried about location, well you just found yourself the best possible location in Rome. The street is quiet and then two small streets away you have Campo di Fiori, one of the most beautiful squares in Rome.
In terms of the apartment, the pictures are very accurate but don't do justice to the charm of this apartment. Its bright, pleasant, airy, clean and comfortable. I slept in the main bedroom and the bed was great. My friend stayed in the little alcove at the top of the stairs and she loved it up there. The sofa opens into a comfi bed and she had her own space up there. Tons of closet room so easy to unpack.
We personally did not have any problems getting hot water but i did have to practice a little to get the water to the right temp for me at first. So hot water not an issue on our trip.
The only small thing that could potentially be improved are the towels. They felt a bit scratchy on the first day.
Lisa was the one showing us around when we got to the place. We had a little bit of a misunderstanding about when to meet up, so just give her your flight number in advance and she will meet you at the apartment. She gave us two keys of the apartment which was amazing. She made my friend's bed upstairs right away and thoroughly showed us everything we needed to know about the place. It seems that she would be very easy to reach and responsive to any problems but we did not have any!
One last thing, it felt safe. At night and during the day we felt very safe in this neighborhood and in the building. I would love to come back and my friend felt the same way. Enjoy!