We stayed at this apartment for 10 days in the beginning of July. The apartment is light, modern and clean, the kitchen fully equipped. It contains everything you need. The shower is a bit narrow and not really comfortable for a tall person like myself.
The wifi worked perfectly. So did the airconditioning, which is really indispensable in this apartment during summer.
The apartment is located outside the city center which isn't a big problem but the path from the nearest metro station (Alfons X) is rather steep so perhaps not very convenient for everyone after a full day spent downtown during summer (a 7 minutes walk going down/ a 12 minutes walk going up). Latest bus from this metro station that goes in the direction of the apartment leaves at 21.00 hrs so if you decide to spend your evenings in the city centre, like we did most of the time, you have to walk back from the metro.
There are some small supermarkets just around the corner and the stunning Parc Güell at walking distance.
I'm a bit surprised that I did not read about this in other reviews but we found the apartment / building rather noisy at times. House rules were on the table when we arrived (not to make noise, no parties and no loud music etc) but we could hear the neigbours talking thru the thin walls, another female neighbour was screaming out loud day and night while obviously having lots of fun in the bedroom, our doorbell rang very often when we were there (and all other doorbells in the bldg as well, felt as if people were ringing the doorbells randomly).
We just loved Barcelona however and we will certainly visit the city again.
I have not met Sergi in person, we just e-mailed a few times before our arrival, we had to pick up the keys at the reception desk of his office (which is on the way to the apartment/taxi can make a short stop there) and he checked once if everything was okay by e-mail during our stay. Overall we enjoyed our stay at this apartment.