If you're looking for a bed and breakfast that is cheap in Madrid, this is centrally located but not the most comfortable place to live. If you're willing to compromise on some common necessities and willing to risk the room being "as per the ad", this might be good. My experience wasn't terrible, it was bad. However I would personally never stay here again. Furniture was either damaged, loose or broken. Maintenance people showed up at my door in the morning unannounced. Not something you want to experience after taking a flight and then commuting into the city.
The up side - very cool and happening location. Centrally located. Room had a beautiful large window that opens up with day bed in front. Common area could be useful if you're travelling with family / in a group.