The room is very well located, and it's easy to walk almost everywhere. The kitchen was very small, but I was able to cook small meals without any issues. The pictures are very accurate and response was quick anytime I needed anything. Bars restaurants, laundromat, supermarkets... everything was a 3 to 5-minute walk. The bed is comfy, the air conditioning unit is good, and essential for summertime in Spain. Check in was done via an app on your phone, which is great.
There are a few things to note. The apartment is very noisy at all times, day or night. Even from 2-5 a.m. there is a bar and glass recycling bins right in front of the balcony, also trucks (garbage, recycling, delivery etc.) are often in the street. I always carry noise-canceling headphones and good earplugs everywhere, so it wasn't that bad.
The internet connection isn't very good, and often dropped, but it works if you're patient (I wouldn't recommend for working nomads).
Also, don't expect early/late check in or check out allowances, as they work strictly during the times described in their descriptions. There's no staff in the building, so they don't hold your luggage till the room is ready (there is a locker inside the laundromat downstairs, where you can store your bags for a fee).
If you are fine with the things above, it's a great place to stay. I liked both the accommodation and Madrid enough that I extend my stay for another week.