We enjoyed our stay at Daniel's/ his company's apartment. It was super clean, cozy and well decorated. There was a lot of space to hang out in the kitchen/living room area and so much space for many people.
I am giving 4 and not 5 stars because
1) You have to send your ID/passport over the internet which we found was not a secure way for such sensible data
2) There is not a lot of equipment in the kitchen - no salt/pepper, no drying rack and no kitchen towel, so we had to use one of the bathroom towels to dry our dishes
3) The remote control of the smart tv wasn't working and we could also not operate the system using the tv's buttons. This was a minor inconvenience though, as we were exploring Madrid a lot.
I've also already informed Daniel about these issues, so I'm sure they will take care of it.
I'd definitely book this airbnb again as it was also very close to the city centre and to supermarkets.