Ines is a very sweet, caring and helpful host. (She even offered to let our lost luggage be delivered to her address so that we could go see the sights.) For English-only speakers, communication must go through a translation application, but she's patient to be sure she understands.
The apartment is as pictured and was very clean. We appreciated the muffins and instant coffee and hot chocolate packets that were offered. Ines even left us some traditional Spanish Christmas cookies under a little tree.
The location is great. The apartment is tucked away on a quiet street but just a few minute's walk to Puerta del Sol, which is Madrid's equivalent to Time's Square, so most of Madrid's sites were within a 20 minute walk. Puerta del Sol has a metro station, so it has access to the airport, although it involves two transfers (and stairs), so it takes about 50 minutes.
The apartment is definitely cozy, but that is to be expected in the center of a large city, and it was fine for four. (I imagine it would be very cramped with six people since the sofa would expand to become a bed and overtake the living room and prevent access to the dining table.) The photos are accurate, but it is worth noting a few points for those with mobility issues. The apartment in general has several areas that require stepping up and down. The queen bedroom is actually a loft, with steep and open stairs and no handrail past the last step at the top, making access a little challenging for those with mobility issues, a fear of heights (there is also an open metal grill to the area below), or who make trips to the bathroom at night. That said, it's a large room with a nice view, so our kids enjoyed the space while we parents opted for the bedroom with the twin beds opposite the bathroom instead.