It's a very disappointing flat in a good location with decent hosts.
First the positives. Host communication was very good overall. Messages were responded to promptly and check-in/out instructions were clearly communicated. Anna (the co-host) seems like a sweetheart and very accommodatingly let me drop off my luggage before the official check-in time, which was much appreciated. The flat's location is also excellent. It's within walking distance to Hyde Park, Kensington Palace, and Portobello Market and right around the corner from the Notting Hill Gate Station (Central, District and Circle Lines), which will get you to ~95% of London's museums and tourist attractions in 30 minutes or less.
Onto the negatives. The place is a bit of a dump, especially considering the price point. The communal hallways are dingy and dark, often full of laundry bags and boxes of cleaning supplies, and the carpeting has seen better decades. The flat itself smelled super musty and I could see dust floating in the air. The ladder used for entry to the loft is literally an industrial ladder and definitely not compliant with UK building codes. The couch is saggy and depressing. The bathroom is comically small, even by UK standards, and there has been no attempt to make the tiny space more usable. For example, there is no ledge in or near the shower, so you're forced put all toiletries on the shower floor. Also, the mirror in the bathroom was hanging off the wall at a jaunty 45 degree angle. WiFi is actually shared with all of the other units on the floor, so its pretty spotty and slow. My mobile WiFi device was often better strength than the flat's WiFi. Finally, the walls are relatively thin, so you can hear quite a bit from the neighboring units if they're occupied.
Overall, the flat was disappointing and I wouldn't recommend it to anyone in its current condition or at its current price point.