Overall we were very happy with this flat in Chelsea, where we two spent May and June of 2016. Here is a summary of the pros and cons:
Pro1. The location of the flat is very good. On a very quiet and lovely street, but within walking distance [a few blocks to about a mile] of many nice restaurants and shops. A Waitrose supermarket is about 1/2 mile away.
Pro2. The flat is on a high floor, and has quite a bit of light. On the latter we were a bit surprised, as the photos in the AirBnB page gave us the impression that the place would be a bit dark.
Pro3. The place is very well equipped, almost anything you might need is there, someplace.
Pro4. The owner is very responsive, and he tries to fix problems asap. For example, we noticed that the refrigerator was not cooling properly and notified him. A replacement unit arrived within a few days.
Pro5. Bathroom newly renovated.

Con1. We knew about this one in advance, so it was no surprise, but it is still a con. There is no elevator in the building and you have to climb several flights of steep narrow stairs to get there. This becomes an issue particularly on arrival and departure with suitcases. The rest of the time it is exercise, which is good for you.
Con2. The flat is a bit overstuffed with the owner's belongings, leaving little space for those of the guests [particularly on a long stay]. But the owner agreed to let us "pack tightly" his stuff, and this was enough to free up space for our things.