We were a party of 8 (although the place accommodates many more people) visiting mid-March. The location was fantastic--less than 5 minutes walking to the train station (Gamla Stan) and within blocks of several pubs, eateries, and cafes, as well as two grocery stores and a pharmacy. We ate breakfast at a different place every morning.
The place itself is well-appointed. We loved the high ceiling (skylight) and the christmas lights strung across the beams. The beds are comfortable, no complaints from people sleeping in the loft or the pull-out sofa-beds, and there were no issues with the cold (just make sure the radiators are turned on!). The kitchen has pots, pans, plates, and glasses if you want to cook.
Definitely pay close attention to the photos and descriptions--the stairs are a little treacherous with luggage and/or socks, and the upstairs bathroom is very small such that no one bothered with the shower up there. This is all well-documented in the photo gallery, though.
Some not-so-obvious things: the bathroom floors are heated and there is a towel warmer in the downstairs bathroom (the button to turn it on is on the underside of the rack). All the round, button light switches also function as dimmers, handy for getting around at night without waking your roommates.
William and Sofia were very attentive hosts and responded to all our inquiries within minutes/hours. The place was clean and ready-to-go when we arrived, and check-in was hassle-free. We all definitely enjoyed our stay. For the price, the place is a very, very good value.