Mario is a great host, and he was flexible to accommodate our check-in and check-out. Communication with him was quick, and he met us in person to show us around the apparent. The place is in a FANTASTIC location; you really can beat it! The apartment is next to Gran Via and 5-10 min walking to the charming neighborhoods of Conde Duque and Malasaña. The place is perfect for spending a couple of days in Madrid if you plan to check out the main attractions. The space is not huge, but it works just fine for one person or a couple.
The only thing is that the apartment has pretty thin walls, and we could hear the neighbors, but apart from that, we had a great stay at Mario's place.