Carlota's apartment is very 'cool'. There is a nice mix of old and new in the design of the flat, and the shared close in the building is well maintained. The apartment is also well situated - a 10/15 minute walk from Sao Bento rail station and city centre, and 2 minutes to Balhao metro station (direct line to the airport). Considering the apartment building is on the main road it is nice and quiet. People who struggle with stairs may find it difficult to access, though.
The one issue I had, however, was communication. I felt I needed to push for a reply whenever I contacted Carlota - two messages were often required in order to illicit a response. When we arrived in Porto Carlota informed us her friend would be waiting for us. We arrived 10 minutes early and there was no-one in the apartment despite being told there was. When said friend did turn up we were told to wait outside in the street for 5 minutes, which ended up being closer to 15/20. We then advised that we would contact this friend the night before leaving to give a departure time and if it suited. No reply. Another text in the morning and once again, no response.
I've been let down by other hosts before so maybe that's why I've emphasised the communication issues so prominently. However, I feel it's important to feel reassured with prompt replies when you're relying on someone for accommodation in a foreign country. Otherwise, a pleasant stay.