We had a lovely stay in this apartment. It's a really interesting space in a historic building. It is very spacious and bright and in a great location for exploring Gamla Stan and other districts of Stockholm, but also reasonably quiet. The bed and the sofa bed were both comfortable. The hosts allowed us an early check-in which we appreciated.
Our one issue (which other guests have mentioned, so it's a shame the hosts haven't done anything about it) was that although this is advertised as an apartment for four people, there is seating for only three people in the living room, and this is on a sofa bed which when in sofa mode tilts downwards so that you feel as if you're going to slide onto the floor. There is plenty of room for another chair or sofa but as it is one of us had to sit on the floor or go to sit in another room.
Other than that we very much enjoyed our stay and would love to return if we visit Stockholm again.