After staying in Martin's apartment for almost six months, I can say that is an excellent option to stay in Oslo. First, he was the only host from airbnb who accepted me for a month with the possibility to become a long term guest. The apartment is located in a very nice and safe area, close to public transport, grocery stores, restaurants etc.
It is also very well equiped in order to have a pleasant stay and feel like home. The apartment has a unique, relaxed and outgoing atmosphere. Martin will always be happy to help you either with the washing machine or with a good restaurant recommendation.
If you want to go to Oslo and know what it is to stay with an authentical Norwegian, you should book your stay with Martin.