The apartment was totally worth it. A small studio with an amazing balcony (fairy lights!) was very spacious, very clean-looking, very comfy. We had the most amazing 4 days in our lives, and if we come to Oslo again, we will probably rent this apartment again <3 The only minus was that the apartment doesn't have a kettle and a microwave, but you can do with boiling pots and frying pans just fine.
It is really close to the center both by bus and by foot, but if you like to walk, I certainly recommend following a river just outside of the apartment building in the city center direction. An amazing walk!