We (2 adults, 1 baby) stayed 9 days in the apartment. In short, it was the perfect place for our Madrid vacation. Everything from the apartment itself, the location and connection to transport was close to perfect for us.
The apartment is very comfortable, has thought-through kitchen appliances for cooking, was really clean when we arrived, and a nice atmosphere for hanging around, dinner, etc.
The hosts were very responsive, we had a few questions that were responded within minutes which was great.
We also got a self-made guide to Madrid from them which was a nice bonus.
From the apartment you can easily explore La Latina, Lavapies, the centre, as well as going to Retiro Park, Prado, etc. Even walking to Malasena or Salamanca is just a 20-30 min walk through the Center.
All in all highly recommended!