Isabel's apartment was our first Air B'n'B experience and I couldn't have wished for a better one! Isabel responded to my emails timely, she waited for us at the apartment when we arrived and showed us around before leaving.
The apartment is perfect for short stays in Madrid - it is airy, bright, with everything you might need during your trip. The noise which some reviewers mentioned does happen, but I think that is the case with most residential buildings.
Malasaña area, where the apartment is located, is perfect for dining out and exploring small streets. It is also close to Chueca with all the bars and night life buzz. But, for those who are not interested in night life, it is close for exploring the cultural offer of Madrid, either by metro or on foot (metro is super easy to use, but we still managed to walk approximately 20 kilometers each day).
To sum it up - I was perfectly happy with the apartment's functionality and proximity to everything, I happily recommend it to future Madrid travelers, and I would definitely book it again!