We went in middle August with two kids. The apartment is big, compfortable for 4 people if they sleep in double beds, and very quiet. The double beds are not very wide, though. It has a huge TV, cable TV, X box (my kids loved that) and some board games.
The place is two metro stations away from the center, and quite close to the munch museum and the botanic Garden. It is in a nice and quiet neighborhood. There is a good supermarket around 300-400 meters away. There is no microwave but there is an electric machine for boiling water.
Finally, the host (Eirik) was really helpful and answered all our questions in few minutes. In summary, if you are a family with 1 or two kids (or two couples) and want to spend a few days in a quiet district of Oslo, this is a very good option. We would go back for sure if we had to visit Oslo in the future.