The unit itself is in a great central location close to several metro lines which is great for getting around Barcelona quickly and efficiently - we used it every day. The location is right off La Rambla and near the Mercado de La Boqueria which was fun to walk through to pick up quick bites and there was a grocery store nearby. The unit was clean, had plenty of space for two people, our washer worked well enough but we had to get creative in finding ways to dry clothes since they ask you not to hang clothes on the railing but we couldn't find a line in the bathroom or a clothes rack.
The initially check-in on the phone was relatively straight forward - we had read other reviews that the app was preferred and the office was far away, however, we did struggle with the app having good enough signal in the building to open doors but we eventually made it. Unfortunately, one of the days during our stay the app stopped working and we couldn't access the unit - we called the office and they sent someone to let us in ~10min wait, we called later that day to ask about getting physical keys because the app was still down and though communication was a bit of a challenge, they did bring us physical keys which we used for the rest of our stay.
I would recommend to use the mobile app for initial checkin so you don't have to take luggage across the city but it might be worth considering getting keys from the owners in case of emergency.