Here's the bad up-front: I was in a first-floor room, on the same facing as a sidewalk and street construction (as of June 2016). It's not going to be the most restful, so if you're a light sleeper, avoid this.
That said, I really just wanted a very cheap, small single room, and that's what I got. If you're going to be very active and touring around, by all means go for it; the added 50 Crowns for breakfast is actually a plus. The best bit is you're very close to everything: one stop from Stockholm Central station, walking distance from Slussen with the lively street traffic along the way. Also, Sodermalm itself is up-and-coming: it's not the "Knife Soder" of the Millennium Trilogy.
That said, the building is old, and the walls are very thin. Again, if you're a light sleeper or are particular, choose another place.