After reading the reviews on Expedia, we did not know what to expect as they were going from an extreme to another.
However, we were very pleasantly surprised by the studio on the 4th floor. The first studio was extremely filthy and the cleaning had not been done, but the receptionist was very understanding and immediately changed us to another place.
While the bathroom severely lacked ventilation, the studio itself was very good. All essential amenities were provided, and the location in Kensington is very central and superb. The hold for the deposit was paid back the same day and the reception was available 24h.
The only things to be wary about are the possibility to have a basement accommodation - luckily it was not the case for us, and the fact that there is no elevator. We were on the 4th floor, and it is something to consider if you have mobility issues.