We were looking for a place to stay for one night after returning to Madrid via train and before flying out the next morning and Airnaldo's apartment was in the perfect location and for the right price. The place was recently renovated (looks like a large apartment was split into 3 Airbnb studios) and was sparkling clean. The description was accurate, the self check in was a breeze and electronic communication with Airnaldo was quick and efficient. I would definitely stay again if I have a similar need for a one or two night stay near the train station.
That said, if I were to stay in Madrid for more nights I would probably look for a place in a nicer area that is not right across the main train station and that has more space and feels more personal.