We spent two nights at Beate apartment and it was great.
It is in Grünerløkka, very trendy place. There are some cafe, bar, restaurant within walk distance. Also it is very accessible to the center of Oslo or other popular sightseeing places by tram, in front of the apartment.
The room is also nice and very cozy. The only one thing I wish for the improvement is the condition of WiFi. Some guys may feel it stressed.. but it was solved after I moved to the point which WiFi is in a good condition.
Anyway, in spite of good location and room, the price is reasonable. I can recommend you Beate apartment as one of the best option in Oslo!