The flat is really nice and in a central location at Oslo (the Royal Palace is just a few blocks away and the harbour is 5-10 minutes walk away). It was clean, Martin was helpful and check in and check out worked very well. The amenities are good.
I stayed for a month and have couple of minor points to make. The building where the flat is located is this nicely renovated early 20th century functionalist building. It has been renovated to be cool and youthful, with all the murals and sculptures you can see in the pictures. The people living there are mostly fairly young and they party hard. There also seem to be a lot of pubs and clubs in the area, which all meant it was pretty noisy during the weekends. If you are looking for somewhere to stay, where you can access nightlife in Oslo, this is a major plus. If like me, you want to work and sleep, it is less of a plus.
Also, the laundry facilities didn’t work that well. You need to top in the Internet, but I lost some euros, when I did it the wrong way and the automat at the laundry room still told my balance was -17 NOK, even though I had just topped up. I did eventually manage to get it working, but not the tumble dryer... which always told I didn’t have any balance. Martin asked for the number of my chip, but the issue never got solved. So, this as a slight warning, if you are planning to stay for a longer time and use the laundry facilities.
These are minor criticisms though. On the whole, I found the flat and the area very nice!