As stated by others, there's both good and less than great.
Good:
Location: close to most everything - can walk most anywhere if you're in reasonable shape
Unit: Big unit with everything you need
View: great view of the castle
- laundry
- 2 grocery stores within a block
- lots of restaurants within a block or 2
- plenty of tv channels when you need some down time
- Hop-on-hop-off stop right on Bread street
Less than great:
- Carpet def needs to be replaced
- no freezer
- definitely a noisy street. If you're a light sleeper this is not the place for you
The noise from the ambulances (why so many??) and the drunks from the bar across the street can be bothersome, but I was on vacation, so I was sleeping in anyway.
Overall I enjoyed my stay. The unit is big and gives you much more room than a hotel. I'm not the most mobile person but I was able to get to bus stops easily, and to the castle and grassmarket. And for the things that were too far, I got a reasonably priced Uber - I don't think I paid more than £10 for rides to the Playhouse and Holyrood. The airport was around £22.
Would stay again.