We spent 2 1/2 weeks in this flat in July 2016, and enjoyed our time. The location is great...a short-ish walk from Houses of Parliament, Imperial War Museum, Westminster Abbey and London Eye. Within 30 minutes' walk is much more, including Leicester Square. There are four key bus routes that come within 3 blocks of the flat that take you many key places. With a 15 minute walk, you can get to a couple tube stops and at least one train station.
The flat itself is smaller than the pictures make it look; the furnishings are a bit "tired" and the area rugs could use a cleaning. The kitchen is quite functional, but small (one cook at a time, please!). The washing machine works great, but is small enough that you'll be doing a load of clothes every 2-3 days. Clothes hang dry. The bigger bed is only the size of a "double" (as we would call it in the USA). It is not a queen or king. As we had only one kid with us, we gave her the double bed and we pushed the two single beds together for ourselves - this gave us more room to sleep than the "double" and in a bigger room. While those beds are comfortable, their frames move and creak a fair amount.
We also heard a lot of sounds from the flat upstairs - shuffling along the floor, doors opening, marbles being dropped, etc.
There is one bathroom, but it is helpfully split into two pieces - Toilet vs. Shower/Sink. This allowed one person to shower while another used the toilet (and washed up in the kitchen sink).
The one key piece of advice I'd provide the Jennifer (owner): Install a "grab bar" in the tub, as it can be quite perilous to step in and out of the tub when taking a shower (the tub is narrow and, like many in Europe, raised up above the floor). I nearly slipped and fell several times. That said, once in the shower, it was nice pressure and nice temperature.
Jennifer was quite helpful before our arrival, with good information on the neighborhood, buses, grocery stores, etc. The one time we had a question for her during the visit, she was quite responsive.
Overall, we'd stay here again...knowing that we are paying less than other spots w/in the same general distance to stuff. It is important, though, to moderate your expectations about the size and quality of the unit.