We did not end up staying in the Garden Studio, as there were other guests there upon our arrival for check-in.
We hadn't contacted the host prior to arrival, as a couple days before check-in, we recieved excellent, detailed instructions for how to access the unit on our date of arrival. The host came out to meet us as we were trying to figure out what to do next, after there was no key in the lockbox we accessed, per the check-in instructions. The host had left a voicemail and sent a message via VRBO the day of check-in, however, I didn't have an international phone plan so did not have access to check these messages before our arrival (was using wifi to check in and coordinate lodging throughout the trip). Although we had confirmation of our booking, had paid, and recieved the check-in information, she cited a system error that must have allowed a double-booking that she hadn't caught prior to that day.
She took us across the street to another property. Since it was already late and we had an early flight, we went with it and figured it would suffice. While trying to get situated, we realized there was no power to half the unit (bathroom and bedroom) and that the WiFi wasn't working. We also were not able to lock the door, so had to leave it open for the night (this was likely operator error, but didn't feel great staying in an unlocked place and would have appreciated instructions for how to use the lock, either left in the unit or demonstrated when we arrived). We messaged the owner (granted, it was late by this time) and did not receive a message back until the following day, when we were already back home. This message said there was a noticeable fuse box in the unit we should have seen and tried. It doesn't seem unreasonable to us that there would be working electricity upon check-in.
In the unit we ended up in, we did not see usable amenities such as a hot tub that were part of the original listing.
Based on our experience, we would find a different place to stay next time in Keflavik. The host was friendly, but this was a stressful way to end our trip in Iceland and frustrating to have paid for one thing and then recieved another, which didn't meet the needs of what we were looking for. Katrin seems like a good host, so if this looks like it may suit your needs, it could be an option to consider. But, we'd encourage explicit communication prior to arrival to know what you're getting and hopefully avoid the experience we had.