The apartment was really comfortable and spacious. One of the best things about it was the location because almost everything can be reached on foot. The communication was excellent, Melvin responded to the messages almost immediately.
The only cons about this apartment were the weak wi-fi signal, and it was not as clean as I expected (the sheets and towels were okay, but there were some missing points on the surfaces of the other furniture in the apartment), but nothing that can not be fixed.
I recommend it to everyone that would like to discover Madrid on foot and not loose time with public transport. :)