We stayed with Blue Star for 3 nights. WiFi was so weak that almost non existence and the exhaust fan in the bathroom did not work for the duration of our stay, it was not convenient when there was 3 people in the apartment. The sound insulation was poor, you could hear people talking from the floor above and the room adjacent to us at night.
There are some merits of the apartment such as location which is second to none. The apartment is located in Zone 1 and within a walking distance from Tube station and national museums. Plenty of restaurants, cafe and shops nearby.
All in all our experience with Blue Star is fair. Hope they will work on the problems outlined above.