The space is as described in the advert, so no surprises there. It's in a great neighborhood with a metro stop literally just around the corner. There are also various shops quite close by for all your immediate needs--including a bakery, fruit & veg shop, pharmacy, and supermarket. The river is less than a mile away, and there's an excellent path for your running and walking pleasure.
I felt quite safe there and walked around quite a bit after dark. There were always a lot of other people out and about.
The kitchen and bath both work well, and the terrace is quite pleasant if the weather is suitable. I would say the apartment is sized well for one person or a couple, perhaps with a young child or two. You could fit three adults in there if you weren't planning to spend much time in the apartment or if you were just planning a short visit.
It's an older apartment building, so you will hear the neighbors. It's Spain, so they'll be up late. Bring earplugs. Also, if you are terribly tall, you might find creeping around on the loft space (where the beds are) to be annoying. I'm 5' 10" (178 cm) tall and my hair just brushed the ceiling as I walked about in my bare feet. That being said, it was still nice enough (at this price) that I would happily stay there again.
Communication with the hosts was excellent. Ana met me there to checked me in, showed me around the apartment, and gave me some suggestions on things to do and see. If they offer to arrange a taxi, do it. It was really nice not having to figure out how to get there after flying for 20+ hours and being sleepy.