Loved staying here and definitely hope to return! Isabel is a very warm and welcoming host. I truly felt very comfortable, as though I was at my home. The bed is small, so if you're over 6.5 feet that could be an issue, but otherwise supremely comfortable. The shower is indeed the best one in the Western hemisphere, and there is a lodger who plays beautiful piano music upon request.
I had worried that the location would be too far out from central London attractions, but actually transport proved to be quick and easy. Buses stop right outside the building, and the trip to South Kensington tube station is fast. There are also some great local places to eat breakfast - I especially recommend "Flour To The People".
Isabel is vegetarian, so if you plan on cooking there, you can't bring any meat into the house. Other than that, she's very relaxed about things :)