We really enjoyed meeting Santiago - he is a really great person who was happy to advise on restaurants (we had a great Argentinian meal on his recommendation) and things to do in Madrid. The apartment is well located, across the road from parliament and close to everything - we were only about 10 mins walk to the Prado museum.
We had a private room and out own bathroom - comfy and clean, we were on the side of the road however so there was a bit of noise overnight from some kind if building works so had to shut the window making it a bit warm. I think the rooms at the back would have been quieter for the other guests.
Kitchen had all the basics and Santiago was happy to share his spices/tea/coffee.
Overall we really enjoyed our stay and meeting Santiago and another nice couple but you can keep to yourself or chat in the lounge as you like.