The pros first: the apartment is well-located in a down-to-earth, local neighborhood. Not good if you wish to be within walking distance to the hypercentre (though it's a direct metro ride away), but we were visiting friends in the area and appreciated the laid-back atmosphere.
Good restaurants abound.
The terrace is great and the apartment has better than average materials.
There is parking close, if you're coming by car, but budget 32€/day and very (very) tight undergrounds. Otherwise, you can try with street parking, but it's a bit complicated and there's not much available to non-locals apart from spots with a 2 hour max limit.
Now the cons: the host is not particularly communicative and left us waiting to check-in on the street without an address or a code to enter the building for half an hour. Worse still, the phone number provided is not a cell phone and basically always goes to voicemail. This was despite several points of contact (initiated by me) right up until arriving at the building, then nothing...
Eventually another person than whom we expected came to let us in. He was kind but spoke essentially no English. We asked for his cell phone number so we could WhatsApp, to which he obliged, but then he, too, never replied to our subsequent queries.
So all this is to say that you should do your best to get everything explained ahead of time and be sure to contact the host often.
It should be noted too that the host was certainly accommodating and granted us a late checkout until noon. So I think the check-in difficulties were just a lack of planning, or maybe an unforeseen difficulty on his end.
As for the cons of the apartment itself, there weren't many apart from the fact that there's nothing provided for your stay. They have little shampoos, shower gels and (tiny tiny) soaps but nothing in the way of coffee or tea, dishwasher tablets, paper towels, laundry detergent, salt and pepper or other spices, etc. We had to buy it all ourselves and then we ended up giving what we didn't use to our friends who live there.
Though only a minor inconvenience, without these things at the beginning of your stay, you're forced to waste time and energy getting them and then you have way more than you'd ever need for just a few days' trip.
Anyway, I don't mean to nitpick but it did impact our trip in the beginning.
Otherwise, the place is clean and well equipped. Beds are fine and appliances are all in good shape. The star of the show is, obviously, the terrace. And it's as great as in the photos.
Overall, the place served us well and we were able to settle in like real Madrileños for 5 days.