Safdar is a really good host and has a modern and very comfortable apartment - especially the bathroom was amazing. :)
You can take bus or metro to the city center, it takes about 25-30 min. However, for Oslo (one of the most expensive cities in the world) the location and the price are quite good. I highly recommend Safdar.
ps: Also I recommend a 24h-ticket because you can visit the islands by ship with this ticket, too.