Just as listed the apartment couldn't be much closer to the castle and the tourist heart of Edinburgh. The apartment worked really well for our short get away for 2 families together. The kitchen/lounge at the front was great for people watching on the street below, though a little small when we all ate together.
Main benefit was the location. We were able to easily get to the main attractions on foot, or using the hop on hop off open top buses that stopped right outside. The drawback of the location was the difficulty parking nearby, and no proper supermarkets.
Overall - we had a great time and would definitely stay there again.