PROS:
Location. Lots of places to eat and drink right outside the door, and two Underground stations within a five-minute walk. The British Museum is so close that visiting is like running out to get the mail.
The unit itself was clean and modern and very comfortable. Lots of towels, cooking utensils, and even little things we weren't expecting, like coffee, condiments and cleaning detergent for the dishwasher and washer/dryer. Onsite housekeeping made getting extras very easy.
Checking in and out was as easy as it can possibly get.
CONS:
No air conditioning, and a little noisy at night, especially on weekends, due to the pub across the street. Not recommended if you're staying in the middle of summer (highly recommended otherwise). The noise is not an issue unless you're one and only priority is solitude and quiet.
Sonder customer support is easy to get in touch with and very friendly, but they failed on a couple of major promises. If you run into issues during your stay, be persistent and firm, or you may wind up disappointed.