Key card NFC app worked intermittently on my Android. Having an apartment that you're not sure you can get back into is disconcerting -- I recommend the physical key if you are worried about this.
The 2-bed apartment was mostly clean and definitely possible to live in for a short time. Neighbors were not noisy, although there is enough street noise and hallway noise that the provided earplugs were a welcome touch. Very walkable to Segrada Familia.