We stayed 2 nights at Javier’s place in probably the coldest possible weather in Madrid. It was -4C outside with rain and snow but the place was really warm.
Communicating with Javier was easy. He was very helpful with everything. Our check-in was quick and informative. The place was clean and it was enough for a short stay. However, it doesn’t have much natural light so if it is very important for you you may want to thing twice. Apart from these, the location was good. It is 5 minutes to the Atocha station on foot and around 20 minutes on foot (7-8 minutes by uber) to many museums and palaces. We havent used the metro but there are metro stations very close.