Mario's Airbnb is located on the edge of a lively neighborhood in Madrid. I loved it there. There are two great places to have breakfast or lunch (Adorado, and Plantaté) a few minutes from the door, both with fantastic avocado toast. The apartment was spotless, with cold water in the fridge, and the bed is super comfortable; even the couch makes a good bed. My tall, 20-year old son was happy sleeping on it for four nights, and gives his two thumbs up. The apartment was a comfortable walk to the best museums and many shops.
Note that, this is probably an apartment for adults-only because there is drug activity on the street. We saw two men doing a needle-based drug in broad daylight on the street. However, we were not asked for money, or even acknowledged in any way. In fact, we felt safe on the streets. Many, many people walk their dogs after dark because of cooler temps. The other thing that might make this best for adults without (young) children is the set of stairs to the apartment because it's up several flights, though certainly not too many if you're unencumbered.
We had issues checking in, which caused stress, but Mario refunded a portion of our first day without me even asking. I thought that was a fair move and appreciated it immensely. For a few nights, I think that you can be very comfortable in Mario's Airbnb, but make sure to nail down the check-in process before you go.