Overall, we very much enjoyed our stay at the Gustavia apartment. We were in the 6th floor apartment and the space was very clean and attractive. It was bigger than I anticipated and is located in a great area. We also appreciated the kitchen, which came equipped with several kitchen tools, including a toaster, oven, pans, dishes, silverware, and even salt and pepper. Overall, I think this location is ideal for anyone visiting Stockholm who needs a comforting space.
There were a few considerations that I think are worth noting. Initially, the communication with Gustavia was excellent. However, at one point the person who we were in contact with went out of town or was sick and the communication was significantly delayed thereafter (e.g. 2 days before a response). I imagine this often isn't an issue, but it was for our trip. Likewise, it appears that typically there is someone present to give you the keys and instructions for entering the space. However, perhaps due to this change in responsibility, we were told to pick up our key from the restaurant located on the first floor of the building, which resulted in some confusion. If you are asked to pick up a key from the restaurant, tell them there is an envelope with your name on it, otherwise they will only give you a dongle to enter the building, but not the apartment. Finally, and this is no fault of the apartment owners, but it appears there is some construction going on across the street. During our stay, the construction banging and chiseling would sometimes start at midnight and go for a few hours and sometimes it would start at 7am sharp. The bedroom faces that direction, so it was by far the loudest space. If you face a similar circumstance, I suggest that you open the pullout couch in the other room and use that instead, as it is far more insulated from the noise.
Overall, I did love the space. It was very comfortable and welcoming and the heating worked wonderfully (which was perfect for those wintery cold nights). I think our circumstances are likely not typical, but I wanted to mention them so that, if others face similar problems in the future, you can have this information at your disposal. I suspect that you would have a wonderful stay at Gustavia and enjoy your time there.