Stayed for three nights with family of 5 (kids 14, 12, 9) for our first trip to London. Location was convenient to Holborn Station (Piccadilly and Central Lines) and the Underground is extremely easy to use; everything is very well labeled. There is a grocery store right across from the station (bring your reusable shopping bags) and a great little pub called Old Nick's on the block behind the apartment. Not sure if they have food but the pints were great!
Building has an elevator to the apartment but there are stairs up to the living room/kitchen from the entry hall. Apartment was clean (I have high standards) save for a little mildew in the shower caulk. Heating system was easy to adjust and was plenty warm. Large window with lots of natural light. Shades on windows were adequate for privacy however if you need it dark to sleep bring a sleep mask.
Beds were an American King, Queen and Twin. There was a roll-away and pack-n-play in the closet that we didn't use. They use removable duvets in lieu of top sheets and there were extra blankets in the closet. The twin bed is in need of a new mattress. Even the 9 year old could feel springs. The twin bed is in a loft within the master bedroom, not much privacy for parents. If you have small children this would not be a good bedroom. Steep steps, no rail or place to block with a baby gate could make this a hazard.
Master bath had tub with half glass shield, not meant for showering. Stand up shower in main bath was very small. If you are a sizeable person you will have to use the tub for baths. Also, no proper outlet in the bathroom. If you like to dry hair in front of the mirror, good luck.
Washer Dryer combo in hall washed well but would not dry (could have been operator error). There was a sizeable drying rack and two stand fans that worked well.
Fully equipped kitchen with dishwasher was great. Only bad part of the apartment was confusing electricity system. Every outlet had a switch and light switches had strange placement so it was not intuitive as to which switch would control which light.
Summary: A few minor quirks but I would definitely choose this apartment again. Owner walked through the apartment at check in and was very easy to get ahold of as well.