5 stars due to: location and hosts.
Location is amazing, at a very pretty street at London zone 1. Everything you may need within 1-2 blocks (subway station, market, shops, bakery, restaurants...).
It is a small place, but the hosts did an amazing job making it comfortable and packed with the amenities one would need in a trip. Also, communication with hosts was great. Instructions were very clear all the way, there is a booklet with instructions and tips of the city, also with quick responses and a true intent to make our stay more comfortable whenever possible.
It is a bedroom/kitchen with a bathroom.
Kitchen is packed with everything we needed: stove, microwave/grill oven, electric kettle, pretty impressive mini fridge (if you set it at max power, will freeze your stuff!).
Bed is comfortable, extra blankets and pillows -- note that one side is by the wall, so access in and out of the bed is difficult if someone else is sleeping at the other side.
Bathroom is pretty ok.. I've seen some much smaller. The water pressure is very good. The temperature gets to pretty hot, but it's not very stable (during the shower you need to keep regulating adjusting as it gets colder, than too hot, and so on). Also, the box floods and your feet are submerged at the end of the shower (water does not fall out of the box though).
Last watch out: we stayed at the 3rd floor of the building with no elevator available. Going up and down (especially with luggage) is pretty tiresome. I would not recommend this place for people with knee issues or conditions that can be aggravated while using stairs to much.
Bottom line is that it's a great place to stay for a few days in London and we recommend it.