I stayed one month at Yuyu's. Just like everybody said in the previous comments, Yuyu really is a very kind and welcoming person. She is always happy to help and gave me some really good recommendations. It was always fun and interesting talking to her and I really enjoyed my time at her place ! The house is very clean and comfortable and the room looks exactly like on the pictures (so it is very small but cute). There is also a lovely garden from which you might get some tasty strawberries if you are lucky enough to come around June ;).
The neighbourhood is quiet and the house is 25 minutes away from a few stations in central london like Yuyu said (Charing Cross, Cannon Street and London Bridge), but it took me minimum one hour to get to most places I wanted to visit (mostly because London is so huge you need to spend a lot of time in the transports, unless you only want to see central London and live in zone 1 or 2). However I have to point out it is in zone 4 and public transports are very expensive in London (but Yuyu's place is cheap for London).
As for London, it is an amazing city and I really recommend spending at least a week there if you have the opportunity!
Anyways, I would have plenty other things to say but I feel like this comment is long enough so I am going to stop there haha...
Yuyu, you know I was very happy to meet you and I will be very happy to see you again when you come to Paris (or when I come back to London) :D