Gonzalo's apartment is in a fantastic location. It's also very comfortable. There's lots of shops close by - in particular a traditional market, only 5 min away and the trendy San Miguel market where you can eat, 10 min away. The area has lots of bars and restaurants but because the apartment is set back from the street, it is quiet at night. All the major attractions in Madrid are walkable from the apartment and the metro is close by.
Having stayed in some other Airbnb apartments we liked some of the smaller items which Gonzalo had included - detergent for the washer and dishwasher and in particular 2 sets of keys. My wife and I do sometimes like to do different things and the logistics of having 2 keys makes meeting up in an apartment much easier.
If you want an enjoyable stay in Madrid, Gonzalo's apartment will add to it.