Just returned from a 5 day stay. The place was terrific and a great home base (2 adults and 2 college students). Location was outstanding with 2 distinct rail lines about 7-8 minute walk from flat. Harrods was also about the same (tip: took the boys to food hall there a couple of times at night. Tremendous variety and although somewhat expensive for prepared foods, much cheaper than eating out). Hyde Park and bus lines only a few hundred yards away as are multiple museums (Victoria and Albert, Natural History, and Science). from a host perspective, Nicholas was tremendous. Knowledgeable, available as needed and even took the time to walk us to a recommended restaurant when we arrived reasonably late the first night.
As much as we loved a couple of things you should know, not they would change our minds about recommending the flat, but to set expectations. One of the bedrooms is tight. We solved this by one of the boys sleeping on sofa in living room. One of the showers is very tight. Kitchen is also very tight with room for no more than 1 person at a time. Living/dining room very ample as was master bedroom (queens beds in Europe not as big as US. As noted, none of this would change us from a highly recommending it, especially given the great host.