My girlfriend and I enjoyed our stay at Carlos & Frank's apartment immensely. It is very centrally located, within walking distance of basically everything in the centre of Madrid. The neighborhood is nice and peaceful. The flat is as seen in the pictures. The kitchen is small but well equipped. The room is big enough for 2 people, but would be quite crowded for a party of 4. The hosts provide bed linen, towels, basic kitchen spices, tea and in the bathroom you have shampoo, shower gel and also a hair dryer. The only down-side is that the walls are quite thin and sometimes the neighbors can be noisy.
Check-in process was stress-free and quick. We used the phone number provided in the listing and Carlos met as at once. He was very kind and also gave us some great advice on Madrid. When the internet stopped working during our stay they were very quick to fix it.
We would greatly recommend this nice flat and kind hosts!