Alejandro is an excellent host, and was always available and happy to answer any questions. We never met him in person, as the check-in/out is all done electronically, but he made us feel very welcome.
The check-in/out system is very easy, you simply open the provided link or sign into the app, and with a swipe the door unlocks. You just need to make sure someone in your group always has a charged phone with internet access. I couldn't get any signal, but after first entering the apartment and joining the Wi-Fi, I was able to use that even from outside the building.
The apartment itself was clean and modern, and looked just as it does in the photos. All listed amenities were included, and basic consumables like sugar, coffee, and oil were provided, which was nice. We didn't do any proper cooking or use the washing machine, so I can't say about that.
The two double bedrooms have air conditioning, which was much needed on some nights. Unfortunately the twin single room and the living room (where there is a large sofa bed) do not. This was really the only downside of our stay. Perhaps it was just because we were returning from the festival (Primavera Sound) in the early morning, and sleeping until the early afternoon, but sometimes it got too hot to sleep comfortably. The addition of air con to these other rooms would be brilliant. Other than this, everything about the apartment was great.
The location of the apartment is ideal, being 30 seconds from a supermarket, and a couple of minutes from La Sagrada Familia, which is spectacular. It's really nice to see it in passing as you go out in the morning to get breakfast. There are many good restaurants in the area, including some vegan ones (La Trocadero, Vegan Mount), so we never had to travel far to find food.
Bus stops, metro stations, and a tram stop are all only a few minutes walk away. The tram being furthest at about 15 minutes. This is then about a 20 minute ride to get to the Parc del Forum, the site of the festival. We mostly took Ubers when we could, as you can easily go to La Rambla or Barceloneta beach for only €10-15. In a taxi (which will be the only cars available at busy times), it's more like €30-40.
In summary, I would highly recommend Alejandro's apartment. It has everything you need, both within, and in the surrounding area, and all for a very reasonable price. We would gladly stay there again, and perhaps we will when the festival comes again!