I travelled with four other adults, as a surprise trip for my fiance's birthday. We loved the fact that the flat was so light, airy, spacious, with high ceilings, it really never gave us the feeling of crowded.
The flat was clean and tidy with every single amenity you could possibly think of, from coffee to toilet paper.
The communication with Frédérique was great, she answered all our questions promptly and after check-in we never really needed to get back in touch because everything went well.
We were met by Ivan, their agent, at the apartment. We arrived way before the check-in time but he was kind enough to allow us to leave all our bags, and we were able to just return later, once everything was cleaned.
While the check-out was early, Frédérique gave us a really good tip about a locker place in Placa Catalunya, where you can leave your bags (super cheap and safe) if you need to travel later in the day. So that worked out great for us. For the check out, Ivan came back to the apartment, gave him the keys and that was that. Please remember to have cash with you for the city tourist tax which you'll pay at the apartment.
The flat is 10 mins walk from the Metro station (guess you could there in 5 but I really take my time when I'm on holiday) and if you keep on going you'll be in Gracia, an area full of bars, restaurants, coffee shops and most importantly: DELICIOUS PASTRY/CAKE SHOPS. It's about 20 minutes walk in the other direction to Sagrada Familia, and another 20 up the hill from Parc Guell.
Really easy process, from booking to check-out. Great value for money and in a quiet but still alive area. All in all, we definitely recommend it for a larger group or family.