Carlos & Frank's apartment was great, and looked just like in the pictures. Even larger than the pictures.
All the facilities were very good - Comfortable bed, great shower, lots of space and very quite.
Frank greeted us warmly and was very kind to us, making us feel comfortable right away.
He also gave us some tips regarding the surroundings - Restaurants, places to visit etc.
The apartment is located in quite a central place, but basically it seems Madrid can be covered by foot from pretty much everywhere. Recommended!