We stayed for about 5 days in Madrid and thought overall the space worked well. It's definitely very small but was manageable as we didn't want to spend much time sitting around the apartment anyways. The location was super convenient to the metro and a lot of great sites that we wanted to visit - just a short walk to the palace.
Fair warning, the door has glass panels that are covered but they are still see-through when you have the lights on at night (we ended up adding another blanket to the curtain rod for privacy). It can be noisy depending on what times you are in the apartment with cars and dumpster noises, ear plugs recommended for any light sleepers.