I'd stay here again. It does have pros and cons. Upsides are significant --- an absolutely fantastic location, a great price for a regularly cleaned, safe central-London neighborhood steps from the British Museum and minutes from two Tube stops, virtually no street noise, good wifi, a nice in-room hair dryer, and a well-functioning washer/dryer and decent kitchen (in the basement right next to this room). The shared bathroom has a very high ceiling and nice natural light from sky lights, which makes it feel much larger than it is. Peter is very clear and very prompt in his communication and his posting is honest and accurate. He got back to me right away each time I asked questions before and during my stay, and check-in and check-out are super easy.
Downsides are mostly those that come with any shared living space or basement room rental, so you've likely already considered them before you booked. If all rooms in the house are booked with both possible occupants, there are six people sharing the one toilet and shower. A few mornings I had a decent wait. There is an open, uninsulated storage space leading from the bathroom and upstairs bedroom down to this room, so almost every night I very clearly heard other people's intimate bathroom and bedroom noises. As others have mentioned, the steps down to this basement room are steep and narrow with a quite low ceiling, and I'd say there are a dozen of them. I'm 5'8" and had to hunch over most of the way, and it was a bit precarious with just the carry-on size luggage I had. If you have mobility issues, are large, or have big bags, this might not be the room for you. As the pictures accurately depict, the room is totally windowless and has no exit or fire escape, so it also isn't for the claustrophobic.