From check-in, we figured that Elena and Nereo were going to be very hands-off hosts. A neighbor of theirs arrived (late) as we waited on the sidewalk with our bags to give us the key to the apartment. We entered the apartment, and there was a short list of information that was not mentioned on Airbnb - this included the clothesline procedures, and the facts that we needed to open windows to ventilate the apartment and empty the bucket used to catch condensation from the climate-control unit.
As far as Vallecas goes, it's an okay part of town. The metro stop is fairly close, so it's not that bad of a commute - it took about 20 minutes (3 blocks and 5 metro stops) to get to the first things in Madrid proper (Atocha) and about 30 to get to the true city center (Sol).
I'd say that just good enough is a way to describe most aspects of the apartment. The wi-fi was slow and cut out a few times a day, the apartment was pretty noisy, but you can count on people honking just about anywhere.
We never received a key to the mailbox, making any orders/deliveries very difficult. Elena and Nereo's apartment was okay for the time that we were there, but after a few days, we did decide to cut our stay short to move to somewhere a bit quieter, more convenient, and easier to maintain - we're studying abroad in Madrid for the semester.
After about a week and a half or two of correspondence, responses from the hosts became more and more sporadic - I believe they went out of town for some amount of time. When they did respond to any issue we had, we were told that a neighbor would come help, but we only saw this neighbor on the first day when we checked in.
These weren't the reviews that we had read beforehand, so we're hoping that we were just an unlucky case, but I would have appreciated a more hands-on, prompt host that was willing to come help us solve any problems we had. As far as the property goes, it is fine for a few weeks, but I would encourage looking for a better location for short stays (less than two weeks) and long stays (more than five weeks).