The good: You really can't beat the location. It's right on the royal mile with easy access to the castle and the train station. The rooms were comfortable and clean. It has a kitchen, which was useful. The wifi worked, and it was nice having a a washing machine.
The bad:
As mentioned in other reviews, there is an issue with the shower. They blame it on the building's old plumbing. But we weren't able to use the shower any morning we were there because too many other people in the building were using it. The issue wasn't that there was no hot water, or just less water pressure.. rather there was no water at all. Because of that we would have to shower at night or during off-hours.
Additionally, water from other people's showers in the building will flow up into your shower through the drain. They have a plug in the shower that is supposedly there to prevent this, but it was a small plastic plug that did absolutely nothing. The water would come in with such a force that it would dislodge the plug, and the dirty water would flood the shower. Quite gross.
As other people have mentioned, there's a LOT of stairs to get to the apartment. We had no issue, but just something to keep in mind.
Also, you enter the apartment through a shady alleyway (close). The day we left, there were human feces in the close.
Lastly, this is one of those listings that is owned by a larger company, not a single individual. So, while communication was mostly quick (during business hours), it typically wasn't someone who could immediately help with any issues.
So, all in all, while it's a great location, we would not stay here again, given the issues. Pay more for a hotel in the area, or stay slightly further away.