Alex and Lati (and Cuore the dog) are super friendly and happy to help both in person and by phone. I stayed with them for a relatively long time (3 weeks) and they really made an effort to make me feel welcome. At the same time they are extremely respectful of privacy and the layout of the apartment meant that we were not on top of each other. The rooms all come off a long corridor. My room was at one end, close to the front door, while Lati and Alex's living room and bedroom are at the far end. The kitchen and bathrooms are in the middle.
The apartment is kept extremely clean and tidy. One thing I would note is that the room is relatively small, as is the window, which looks onto an internal courtyard of sorts, which means that there is relatively little natural light. There was a heat wave when I was in Barcelona and the apartment can get very warm as it is not air conditioned, although there were two fans in the room which made it more bearable and possible to sleep at night.
The location of the apartment couldn't have been better from my perspective. Only about twenty minutes walk or ten minute cycle to the beach, walking distance to El Born and the city centre generally, right next to the parque Ciutadella, but also very quiet and relaxing to come back to after a few hours in the city centre.
I would definitely stay here again.