We have visited Barcelona for 5 days during New Years' week and all of us, my three children, my wife and myself enjoyed it very much.
Anna was a very kind host. She welcomed us very warmly despite late arrival and a delayed flight, she had prepared a gift for my youngest daughters birthday (which I just briefly mentioned in my first mail) and during our stay she asked several times of all was going fine.
The flat itself is an excellent starting point for exploring the city. It is situated in a none tourist area (old factory buildings that were refurbished). Convenience shopping, restaurants and - of course - the beach are just minutes walking distance. From the beach you can access the harbor within 25 min watching people play beach volley or surf, even in December and January. You can also rent bikes or scooters and do bigger tours by yourself. If you don't want to walk, then the metro line 4 is 3 blocks away (7 min walk). Thus, a very nice location, far from the mainstream tourist areas yet still close enough to get wherever you want walking or by public transport.
The flat itself corresponds very well to the pictures. It is, in fact one big room, where the bathroom separates the main part from a semi-closed 2nd room. It's perfectly equipped to eat at home, has a large screen TV (where there is 24h BarcaTV for the football fans), a washing machine, dish washer and everything else you might need. Wifi and AC work perfectly. We did not use the terrace but I assume that during spring and summer it is very nice to have this private outside spot making the flat appear even bigger.
Highly recommend this flat, very suitable for families.