Had a great stay and would stay there again. Was a bit skeptical toward the whole "we send you codes without reception" system, but it worked great. I got the electronic messages on time, instructions were easy to understand and there were no unpleasant surprises. Pro tip - write down the entrance codes on a piece of paper and have it in your wallet in the case you forget your cellphone, or it runs out of juice.
Here are some pros and cons of our apartment:
Pros: Great location ,close to shops restaurants, etc. Also 20-30 minutes walk to the major Madrid attractions, highly recommended. The place is brand new, clean, fairly comfortable for its size. Good beds. High hipster-factor :-).
Cons: Moderately noisy, at the 4th floor in a typical Spanish pedestrian street (I was able to sleep without earplugs). Sun in the morning, no problem in February, but it might be the problem in summertime. Relatively small and no dishwasher in the studio (although there is one at the common kitchen). All in all, very happy with the stay. Price taken in consideration, extremely happy.