My daughter and I stayed in Catherine's flat (ground floor of a house) during the heat wave in July. The house has lots of character, beds are very comfy and the kitchen was well equipped to cook meals. Wifi was good, garden spaces were pretty, especially the oasis out back.
The heat wave affected both our plans and mode of transportation. Busses and the Tube (which we had planned on using) were basically furnaces and not recommended so we relied on cabs. Black cabs are pricey and because of the location, it cost us over $120 CND for one trip downtown and another one back. We also had cabbies refuse to take the ride because they didn't want to go that far so it took us 50 min to get one after a night out at the theatre. Portobello Market and grocery stores, are all about a 15 min walk.
If you plucked Catherine's place up and put it closer to downtown I would definitely stay again. But because of the location, that changes things for me. That being said if you are looking for a quiet getaway spot, close enough to Portobello for restaurants and great shops to poke around in, this would be perfect.