I stayed for 10 days and worked while there. The apartment is right next to a bus stop with buses that come every 10 mins to get into the centre, from the centre you can get pretty much anywhere in Oslo using another bus or the metro. You can get a week's pass for all public transport in Oslo (zone 1) for roughly 800 krone.
The dedicated workspace was okay, however I mainly just worked from the sofa/bed as the chairs are quite uncomfortable and seem like they might break (I'm quite heavy :)).
I didn't eat out while there as the prices are very expensive for someone from the UK (roughly 80% more expensive), however the kitchen is equipped with everything you need to eat in. There is a Kiwi supermarket 5 minutes walk from the apartment that has everything you will need to eat in, and the quality is great.
Mauro made the check-in easy and communicated at every step as required. Mauro is a great host.
Sleeping in the apartment was without issue, the bed is very comfortable and the apartment block is very quiet, however you can't sleep with the window open as the road next to the apartment is very noisy.
Overall my stay was great and I would definitely stay there again if I visit Oslo again.