We had a good time in the apartment. We mostly communicated with Carlos' brother and co-host Jose (under username Tono). They went out of the way to provide us with a travel cot and baby chair which both were tremendously useful. We did not meet them in person, but that was fine, everything went smoothly.
There were two bad reviews from guest before us. They were not baseless, but Carlos and co. made efforts to fix the problems. With a new, powerful air conditioner, the dampness is gone, and related problems (mold, smell, cockroaches [mostly]) have been fixed. The apartment smelt good and there was no mold. We encountered a single living cockroach (not living very long, mind you), and two already dead. Given how many dead specimen we saw a few streets away, they may well be a fact of life around these parts. The temperature and humidity in the apartment were absolutely controllable despite the outside weather conditions. The plumbing problems were handled by Carlos and Jose using some MrMuscle, but that proved to be not entirely sufficient. After using the washing machine, we, like earlier guests, experienced water coming up the bidet, and slowly draining sinks. So this problem persists, but I am sure the hosts can get a professional to fix it.
Otherwise, the apartment is cosy and stylish. It is not exactly located in the Russafa block, but near enough. It is not on the beach, not in the city centre, not next to the City of Arts and Sciences, but all of these can be reached very easily with Valencia's great bus network in a 10-30 minutes. There is a large Consum supermarket, a Chinese shop selling everything, a Chinese-owned cafe with cheap but fine coffee, two playgrounds, and a tobacco shop selling EMT cards, all within 100 meters. The supermarket is especially great if you plan to do your own cooking. BTW, the kitchen appliances (microwave, fridge, freezer, cooker, cooker hood) are all top-notch and operating flawlessly.
All in all, the hosts appear to be working hard to provide the guests with everything, and they are battling the emerging problems with some success. If they manage to fix the plumbing, the apartment will be a great value-for-money choice.