We had an excellent time at the apartment. It is an "interior" apartment on the ground floor and therefor rather dark. As we usually spend most of our time outdoors that's not an issue at all. The apartment being situated in the building where it is makes it a rather quiet apartment. There's no city noise!
Our experience with this apartment is the best we have had using airbnb in Madrid. The apartment layout is excellent, the apartment is nicely decorated and clean, response to messages is prompt and the (very small) problems we encountered were solved swiftly. Hans is a real pleasure to deal with too.
I would highly recommend this apartment. It's situated rather ideally. Museums, restaurants and bars are nearby (a nice cafe (Libre) to have breakfast or lunch f.e.) and if you don't mind to walk a bit, the city center is within walking distance too. Atocha railway (and bus and metro...) station is nearby as is Lavapiés metro station.