The contact was very nice, and flexible with our shifting arrival time. The apartment looks very true to the ad, simple but clean, nice and generally well equipped, though a bit cold (one small radiator, bed in front of window, cold stone floors - probably great in summer, but not in January).
I had picked the place mostly for its proximity to some museums and Atocha Station, which in fact was perfect walking distance. I think the apartment is best for people who look for a place to crash while plunging into the nightlife. If you want to get some real sleep, be aware that there will be a lot of nightlife right outside the window (I can only speak for a weekend experience).