My wife and I stayed here for a few days while visiting friends in London.
Clerkenwell as a location is great - tons of great pubs nearby, as well as restaurants on Exmouth Market a 2-min walk away. Superb transport links too; lots of busses run right by here, and Farringdon station is really close. However, you are pretty close to a busy road, and when we were staying there there was a pretty large & noisy construction site right across the road.
CityLiving left us all the usual amenities and we were pretty comfy in the flat. It's fairly basic furnishing-wise, but was a bit cheaper than other 1bed airbnbs in central London.
One slight issue is that the touch-pad door-lock was tricky - took us a few minutes to figure out how to activate it! Worked fine once we got the hang of it.