I stayed at Mark's place with my two children for 6 nights. We had a room and the bathrom on the upper floor and used leaving room and fully equipped kitchen on the second floor. Our room and bathroom were isolated by two doors from other parts of the house. It was very quet though the house is just on the Portobello market.
Room was very convenient and clean. All the things that tourists need were there: from USB chargers connectors to multiple London tour books.
Mark helped is with all the questions we had. He even bought my son the batteries for his new toy.
The location is very strategic: not far from main London attractions, parks, supremarkets, metro, restaurants are very close. I'll definitely stay at Mark's place another time.