On the plus side: In terms of value and location, I had a great stay. I was able to stay in the city for a nice long time because the nightly rate was so low. Also, the flat is SO close to the Notting Hill Gate tube station, which is right along the Central Line (which goes straight through the heart of London) and the Circle Line (which goes around the edges), which is a major plus. It's also right around the corner from a lovely bakery, Paul Rhodes, where an inexpensive breakfast can be had for about five quid.
Onto the critiques: As I was on my way to the flat on the tube, I got a message that the room I'd booked was actually unavailable due to a plumbing issue that would take a few days to resolve. I was moved to another studio on the top floor (the room I booked was in the basement), which was quite a shlep up to. The room was fine, generally clean but basic, but the walls were a bit dingy and the shower shot streams of water straight out when i turned it on each time (it took some maneuvering to make it work).
Fortunately, after three nights in that room, I was moved to the original room I'd booked, which was quite a bit nicer (fresh paint, nice new furniture, and steady shower). I will say that Billie was VERY communicative. I never felt left in the dark, even if an adjustment was necessary. Honestly -- for the price, and for the location, I was happy to have a clean room in a prime location and was willing to be a bit flexible for the sake of my budget. That, I would say, is the mindset one should be in when booking this flat. It could be that your stay would be event-free, but it could be that you'll need to shift around a bit or have a bit of an inconvenience (Max and Billie have the whole building, so it seems that they can shift rooms around as needed).
There was really nothing BAD about my experience...it was, as I had hoped, an inexpensive room in a good location.