The apartment is well equipped and has everything you need for a nice stay. It might not be big, but if you plan to visit the city and not stay there for the whole day, it is perfectly fine for 4 people.
The apartment is not in the city center, but it is close enough to be able to walk back and forth to the main touristic areas, or take the tube there: the stops for lines 3 and 2 are really close by.
The host is very precise and provides all the information needed to get your keys and check in.