All around great experience. Great host, with excellent English communication. Awesome location, right next to Atocha and close to several restaurants. We simply walked to several of the main locations in Madrid. Apartment is exactly like shown in the pictures, and it was perfectly clean.
Be mindful when traveling with large suitcases — the apartment is intentionally compact (but very well planned!) and if you are taking the train you’ll have to go walk up/down several floors of stairs within the train station.