Staying at Kirstis and Helges apartment was an absolute pleasure. It is as stylish, cozy and clean as possible. I think it is one of the most well kept and best equipped holiday homes I've ever been to. Helge and Kirsti are very are welcoming, reliable hosts and communication with them was uncomplicated.
Their place is located in a lively yet quiet and safe neighbourhood. Supermarkets, cafés etc. are nearby. Birkelunden bus/tram station is only a few minutes walk away and you can the city center from there comfortably.
I would definitely recommend anyone planning a trip to Oslo to stay at Helge's and Kirsti's apartment (and also enjoy the great view over Oslo on the balcony).