I was the only guest in Karin's spacious apartment, staying in a room normally occupied by one of her young sons (he was staying with his grandmother). The bed was fine and the room slightly larger than many colleagues who were staying in local hotels. There was plenty of Lego to play with, but I was good and didn't....
The shared bathroom was fine and nice and clean; there was also a separate toilet. There's no TV in the flat (which I think is a plus point!), but WiFi access was fast and reliable, and I was able to link my iPad to her Bluetooth speaker.
Karin was a friendly and helpful host; interested in alternative living styles and a vegetarian. I was allowed to use up food from her fridge, which meant I didn't need to buy so quite much from the nearby supermarkets! The ICA has an excellent salad bar and is open until 10pm nightly.
The flat is in a safe area and was quiet, apart from occasional building site noise as they were renovating the courtyard between her block and the next one. The main room overlooks parkland with water beyond; there are trees visible from a slight angle from the bedrooms, too. There's a small public bathing place about 200m from the apartment, but the water in mid-June was still very cold. There's also a Citybikes rental station about 150m away on Hornsgaten. And it's a great place to start a late evening jog around the edge of the island.
Hornstull is well served by public transport - both T-bana to the centre and by bus (no. 4 is useful and runs frequently until late at night). It's also on a direct bus from Arlanda airport - but on arrival make sure you get on the correct bus - it's not the one to Stockholm Centre but the one to Liljeholmen that you need - if you scan your ticket on the wrong bus it can cause trouble going back again, as they think you have already taken a return journey.
I'd certainly be keen to go back next time I'm in Stockholm.