For context we are frequent travelers with 2 parents and 2 teenagers.
This is a corporate owned building with several flats. Stayed in flat 6. We booked many months ago so received a nice discount off of current rates, and the landlord did honor the reservation (we had another rental cancel because the owners could get more money post covid). Overall the quality was appropriate for the price.
Pros - Location, location, location. Quiet street in upscale diplomat row (next door is Iranian consulate). Beautiful neighborhood, natural light inside if you get a street side flat due to 2 large walls of windows, secure building, easy access to Tube, Starbucks, Boots pharmacy, and Whole Foods within 5 minute walk. Had a minor maintenance issue which they fixed very quickly. Air conditioning worked well, each of the 3 rooms had their own thermostat which was great (use the bottom one to adjust temp). Some basic soaps and such to get you started. Both bedrooms have nice storage and closet space. Host was easy to communicate with.
Cons - parking may be challenging. Walls are thin so noise carries. Furniture is well used, beds are of poor quality, especially sofa bed where springs almost poke thru mattress. Balcony doors only open partially for air, both doors had heavy plants to block one from stepping onto balcony itself (guessing this is by design for noise or safety). Not all flats have balconies, and the inside window opens to a narrow alley crowded with pigeons. There are only 2 trashcans outside that get overloaded so trash just gets dumped alongside and it gets rained on. Limited kitchen items (3 forks, 4 spoons, 2 pots and 1 skillet for example).