My wife and I have been traveling in Airbnb's for several years now. One thing we've noticed is that you can immediately tell the difference between investment properties and apartments that were actually homes. José and María's apartment was obviously their home before they moved closer to the kids' school. The physical space has a livable flow to it, you can actually cook a meal in the kitchen and the morning light is wonderful. The bed is very comfortable and the neighborhood is remarkably quiet.
José and María were excellent hosts. We arrived earlier than expected but the keys were available and José came by later to make sure we were settled in. They have done an excellent job of providing guest information in Spanish and English. This includes local restaurants, grocery stores and where to get boarding passes printed. They were also very quick to answer emails.
The apartment is well located. Ten minute walk with wheelie bag from Atocha. Fifteen minute walk from Prado. Ten to the Reina de Sofia. Maybe five to Retiró. The local neighborhood is also interesting, with some very good wine shops and restaurants. The dry cleaners at 10 Paseo de la Reina Cristina does 12 Kg of wash for €12 (a godsend to people as lazy as I am).
The little things that I appreciated: We were only staying three nights but José and María provided extra towels, linen and blankets. The kitchen was actually stocked with spices, coffee and several types of tea. The water heater has enough capacity to take a legitimate shower.
One note, when AirBnB sends the address, if you just click on the 'open in google maps' option it gives the wrong address. Google shows number 8. The actual building is number 10.
Definitely recommend their apartment. Am hoping it is available next week when I am back in Madrid.