I've stayed in Sonder before elsewhere in London so understand the concept. The property was easy to find from the street and had been renovated well. I received a wonderful greeting at 10pm in the evening from the lady on the front desk who made me feel welcome, and other members of staff I spoke with throughout my stay were equally friendly and very willing to help guests.
The room in the main building was comfortable, with air conditioning, a safe and a chiller – safe and chiller are often omitted by other hotels at similar price points, so this is to be noted positively. I had everything I needed for a comfortable stay.
Downsides. I had read the reviews before booking which seemed to give a mixed perception of the hotel. While initially I could see no reason for some of the negative reviews, the reasons did emerge as time went on – when going to sleep, I realised there is very little sound isolation from the corridors and adjacent rooms. I could hear every movement of people coming and going, so I do expect rooms on the staircase would be disturbed by luggage being moved around by other guests etc. There is a somewhat busy street nearby which seems to be used by fast, noisy cars in the night and this was also audible from the room. I was able to sleep well once things quietened down but these factors from other reviews are true.
In the vicinity I also note that nearby tube stops are some distance walking, although there is a regular bus service (including night bus).