Apartment was fine. A few comments:
Basic paper products were lacking, there was less than half a roll of toilet paper, an almost empty box of tissue and an almost empty roll of paper towels; hosts were unwilling to provide more. Having to go and buy these basic necessities was the last thing we wanted to have to do while on holiday.
Location was not in the best part of Marylebone.
For US guests, be aware that a UK king bed is equivalent to a US queen.