Very large, comfortable flat; probably one of the nicest places we've stayed in our 3 weeks in the UK. It's a fair hike into both Old Town and New Town, which are where the sites of interest are concentrated, but we're good walkers and had no problems. If walking is an issue for you, you'll want to use the bus or tram (once it's running again).
The only problem we experienced was with parking in the area; there was a TON of construction going on in and around this part of Edinburgh during our visit (early October of 2022), and much of the street parking that would normally be available was off-limits. If you are planning to drive, you might want to contact the host in advance and ask for advice on where to park as this created some headaches for us.