My husband and I stayed here for 12 nights in June.
Pros: This place is in a great location, right on top of a metro stop. Next to a great market (Mercado de Anton Martin) for buying fresh food for cooking. Walk-able to basically all the tourist sites. Kitchen is reasonably well equipped for making your own meals. Washer and dryer is great for laundry. Place is spacious so you never feel cramped.
Cons: Host is very unresponsive, an incomplete address is given on airbnb, if I didn't prompt the host I would have just been directed to a large street. During check in host was unresponsive, I called 4 times, and after 20 minutes he finally picked up. Afterwards when I sent a follow up message about check out procedures I never got a response (this was 36 hours before we were planning to leave). The hot water heater has some issues (needs to be reset periodically). The worst part was the sewer smell. I believe this is because we were visiting during a hot period during Madrid, one of the bathrooms smelled quite strongly of sewer which permeates throughout the apartment. I'm surprised I only found one other review (in another language) that mentioned this.