yes, i have - we used it for one night for our London 2012 paralympics trip

. The hotel had only been open as Tune hotel for about 6 months then, I was very impressed, and it was an absolute bargain too.
We had a basement (windowless) room, I thought that would be weird, but it really wasn't. Its boutique-style (ie small and compact) - we had a comfy double bed, with room around one side and at the end of the bed to walk around, store your case etc. There was a narrow tall unit with hanging space, a few coat hangers, and a shelf for your clothes if need be. The remote control for the TV had its own little shelf near the end of the bed, and there was a bedside table/shelf too. The bathroom was compact but fully furnished, with walk-in shower, toilet, sink, towel rail, mirror and shelves.
Reception has a left-luggage area, coffee machine, and lounge area with wifi etc.
Its on Grays Inn Road, just a minutes walk up from the Travelodge there

, and opposite the Click hostel.
eta - based on my raving about the good value of the Tune hotel Kings Cross, several of my colleagues have stayed at the Edinburgh one too (they had an opening deal) and they would all go back there as well.