The stay was good, but felt we got less bang for the bucks (this is Madrid after all) compared to other cities we visited. Cleanliness of cutlery and dishes could have been a bit better. The shower doesn't fix properly so one has to hold it with one hand. It's all a bit tinier and harder to move around in the apartment than the pictures suggest, because it's full of "stuff" and no obvious place to put or store the luggage.
Other than that, Mario is very responsive and helpful, and the location can't be beat as you're right in the heart of Madrid's city centre and every neighbourhood can be easily reached on foot. There's also the metro right in front, if you need one.