My stay (at both the downstairs flat and one of the first floor rooms) was overall positive, but not quite perfect. Both hosts were quick to respond to my messages and dealt amazingly with my particularly inconvenient situation (my flight was delayed by 12 hours and I ended up getting to the city late at night), they were generally readily available and happy to answer any questions.
The shower was wonderfully pressurised and the flat was decently equipped (there were no pots but we didn't notice the need for anything other than that). The wifi is great and the street - while a bit noisy in the morning - is quiet at night. There is also a nice market a couple blocks away from the house, and a tiny convenience store literally next door.
That said, it should be noted that (as of 14th of May 2018) the lift listed in the ad is broken (and it appears to have been so for an extended period of time) which means that if you are looking for an accessible place, this may not be the one for you (do of course check with the hosts because the problem may be fixed in the future). It should also be noted there is a small set of steps (three) from the atrium to the 'ground floor' flat, which wouldn't have been reachable with the lift regardless. Buildings in Barcelona are often not particularly accessible and this one does have the advantage of having a small amount of stairs and large spaces in the flat for one to move with mobility aids if need-be.