The best thing we found about this place is how central its location is. We could just walk to most places of interest and otherwise, we would take the subway, which is also a 2 minutes walk away.
Also, Madrid get very hot in the summer and the air conditioning in the apartment performed really well, keeping it nice and cool and also being rather silent. That was a big plus.
The place itself is nice, but a lot of the space feels quite tight with low ceilings everywhere and small showers (one is small, the other one is microscopic). People who like a lot of space should refrain from booking that place, otherwise, some could find its "cosy" aspect charming.
Communication with the hosts was generally great with a quick response. However, if you'd like a second key because you are more than 1 guest, I would mention it upfront because we had to wait for them to bring it to us on day 2, after requesting it on the first night we got there.
Other than that, the place was tidy and clean, just as we'd expect when checking in somewhere. Overall a good place to stay, especially if, as I said, you don't mind tight spaces.