The flat is small but well enough for a couple and perfectly organised. There is a very good documentation, of everything (that was useful for the check-in, with all the pictures of the path to follow). Third floor, with a clear view. Lots of shops around.
I was a bit disconcerted by the fact that, although the flat is where the owner lives, communications is through an agency, which asks many private questions, and directs the user to yet another Web site (Houst) with more personal data requested. The agency did not react well to our special requests (but one, the demand for two sets of keys, was finally handled, thanks).
When the public transport works, the place is well located, just a few underground stations to the city center and three different lines (Underground, Overground and bus 18) . When there is trouble, such as strikes, the place is quite far away and you have to walk. (Of course, it depends on where you go in London.)
The noise of the trains nearby is quite strong but I discovered you get used to it very quickly and it does not prevent sleep. When windows are closed, the noise from the busy street is fine.
I suggest following the advices in the documentation about the nearby restaurants, they're quite good.