The good stuff: Location is incredible, apartment is well-stocked with what you would need to cook and clean for a week, it's comfortable, the outdoor area is rare for Stockholm and really nice, it's a solid place to stay.
The less good stuff: The apartment could be cleaner. As there is no cleaning fee charged, the tenant is tasked with the responsibility of cleaning the apartment, so while it wasn't visibly dirty, relying on the cleaning of each successive tenant doesn't exude lots of confidence in the cleanliness of the apartment.
We had booked a week stay for 3 people, and there were only 3 rolls of toilet paper stocked. Going out to buy toilet paper isn't the biggest deal, but is still a small annoyance.
The place is nice but a bit run down. For example, the dishwashing machine works, but falls out of the cabinet when you open the top drawer, which is both annoying and potentially dangerous, particularly with small children. In the same vein, there is a large cabinet in the children's room that does not stay closed without a lot of messing around, and then if you do get it shut, it slams open with you open any of the clothing drawers. I took two serious shots to the head during my stay, but fortunately my 3 year old escaped unharmed. It was, however, a constant worry during the stay.
If you need 3 bedrooms (with kids!) and want to stay on Södermalm, this is a perfectly fine place to stay. There aren't very many spots that satisfy those requirements, so if you need that, look no further, just be aware of some minor issues.