This small collection of bakeries is well reputed. On a short city break in Oslo, it makes good sense to stop through one of these. Sure, bread isn't a particularly Norwegian specialty but Scandanavia seems to do it particularly well as I've tasted in each of the restaurants that serves it as a complimentary. Additionally you can use this place as somewhere nice to stop and have a coffee, calorie hit and breather, as well as get some goodies to take away to eat in the park overlooking the Palace and city nearby. Lastly, it is more affordable than any cafe/restaurant for lunch you might otherwise be considering.
I had a croque monsieur which was standard but satisfying. It wasn't the best quality ham nor the cheese as strong as I'd like, but my stomach still appreciated it. I also had a croissant for late which was decent (not as buttery as the best I've had) and a muesli/seeded roll that was a great afternoon (and breakfast the next morning) snack.
Next time I would order the cinnamon buns. I didn't realise this was a particular special of these bakeries, so would have to try it if I was back again. Otherwise I'm sure it won't be too difficult to find something you like.