Great place in a very central location, comfortable beds and good showers. Nice lighting design and industrial feel. Very effective heating, which we needed as the weather was very cold! Downside was some noise from the street and other apartments in the building - worse some nights than others. Also nothing at all provided in terms of salt/pepper/cling film/foil/oil etc - if you are staying a few days only you don’t really want to buy these things.
Also the flat, as described, is on the second floor without a lift and the stairs are quite uneven so it definitely wouldn’t suit anyone with mobility issues!
On balance though, a comfortable option for a stay in the centre of Madrid.