I stayed for two weeks and a half at Maria's place and had a great stay. The place is clean and comfortable. It is located in a quiet neighborhood at about 20-30 minutes in subway from the city center (depending on where you're going), but all amenities are accessible within a 5-10 minutes walk.
Maria and Carlos were very helpful. They transported me from and to the airport for a small fee, showed me around and gave me maps of the subway and city centers, along with touristic pamphlets of interesting places to visit in Madrid.
At first, I was a bit anxious, because they didn't speak a lot of English, and I spoke only a bit of Spanish, but we managed to communicate together as needed and it ended up being an excellent learning experience at the same time!
If you want a quiet, comfortable stay, not too close but not too far either from the city's noise and activity, this is the place for you.
Muchas gracias, Maria y Carlos!