Used John's 3 story apartmentfor my mums hen do, there was 13 of us. It had masses of space and despite the size kept its warmth as it was very cold out.
We all managed to get showers in the morning which I didn't think would happen due to so many of us but the water stayed warm. Only downside was there was only one main bathroom and another en suit, but there was a toilet on each floor.
It was value for money, and so much better and probably worked out cheaper than staying in a hotel.
The location is a 10 minute walk from Haymarket Station and then 10 minutes onto Princess Street so ideal.
Would highly recommend for large groups and would use again in future.