Perfect stay! I was there for 2 months (the coldest ones) and the appartment was really comfortable. It is the right size to make you feel at home, with everything you need and a private bathroom with heating floor (which comes handy in the winter). The heating of the rest of the appartment is nice, and the bed quite confortable. Enough storage space. You share the washing machine and entrance with Kirsti but there is a lot of privacy.
Furthermore, it's location couldn't be better, just 2 minutes walk from a bus which takes you to the city centre in 20 minutes and works 24/7, next to a nice park for a walk and a lot of stores with large opening schedules.
Kirsti is really nice and available but also lets you have your own space if needed. I will repeat my stay there when back in Oslo!