I, along with 3 friends, stayed at Karen's place one night during a visit to Edinburgh. The best thing about our experience was actually Karen herself! She's an energetic, funny and generous host who welcomed us with warmth (although we came in rather late) and showed us every detail of the apartment, as well as recommandations for sights and nightlife in the area.
The apartment is huge and accomodates 4 people without any problem (2 twin beds, 1 double bed, 1 convertible sofa) - the kitchen is also huge, clean and well equipped. Looking out the window you'll have great sights on the Castle! Only the warm water flow in the shower could be improved.
Location, location, location! Karen's place is steps away from Victoria Street, where you'll find great pubs, and the Royal Mile where all the sites worth visiting are. If you want to get to the other side of the Castle (bus and train station, Parliament, clubs etc...) it's only 10mn away by foot.
Overall a great experience, we will come back, thank you!