This is really one of the best Airbnb experiences we have had. I was a little worried as we arrived during a really bad heatwave, but it is an old building with thick walls, Aircon and fans in the bedrooms, so we kept nice and cool.
It is really a fantastic location, you can walk anywhere in the old town. We never used public transport and walked everywhere. It is VERY close to the Plaza Mayor, and the lovely (but expensive) Mercado de San Miguel.
Ruben met me personally and was easy to contact for advice. Definitely much more personal than most hosts.
I would highly recommend this for a few days in lovely Madrid.