Spent a week here starting from the early May bank holiday weekend. It was exactly as described. Clean, comfortable, quiet, and well-situated. Perfect for a couple who intends to spend most of their time out sightseeing and mostly needs a place to sleep, shower, and relax a bit at the end of the day. The location is great for hitting the tourist spots of central London. The Queensway, Bayswater, and Notting Hill Gate tube stations are roughly equidistant, providing quick access to the Central, District, and Circle lines. Connecting stations for the primary north-south lines are just a few stops away. We easily walked to the famous Portobello Road market.
This place is shockingly quiet for being located within a block of Bayswater. The church across the street silences its bells sometime around 9 or 10 at night, so you needn't worry about being kept awake. The hostess lives in the townhouse above, but we were barely aware of each other's presence during our stay. Elena and her assistant Julia were helpful and communicative, though we had no real occasion to interact after check-in.
This is a basement flat, so bear in mind two things: first, obviously there's not much to look at out the window, though plenty of natural sunlight gets in if you put the shade up; and second, access is by some fairly steep and narrow outside stairs, so this flat is a no-go for anyone with significant mobility issues (or for a pram/stroller). Both of these should be obvious from the description, but bear mention. Mobile phone reception was good despite being underground.
Would we stay here again? Absolutely and without hesitation.