On the positive side, the location is excellent. Everything that we wanted to do in Madrid was in walking distance from the unit. Also, you are in the city but it’s quiet at night. The electronic key worked well for us and meant we didn’t need to worry about carrying keys.
On the negative side, it’s not a place to stay if you’re going to be there more than a few days as amenities are not set up for longer stays. Specifically, consumables are limited and you would need to wash/dry towels and sheets since there are no spares. Washing and drying is tough because you would need to purchase your own detergent (not supplied at all) and drying takes long because the unit gets no natural light. The lack of natural light also gives the unit a cave-like feel. Furthermore, the bed is bowed and uncomfortable, the couch is uncomfortable, it was not fully cleaned and the hot water was limited to 2 short showers. In all, it’s not worth the price.