The apartment is perfectly located. Retail shops and restaurants are available almost downstairs and it is virtually 15 min walking distance to Trafalgar, Piccadilly & Regent's street. If you fancy going for a run: put your shoes on and enjoy a tour of Regent's park (8 km back and forth - really nice run). If you're more of a museum person: not a big deal, British Museum is virtually next door on the other side of Russel square.
I was just about to forget to mention that Russel square underground station is just opposite side of the street from building's entrance and there is a car park available (20£/day).
That said, the flat itself is fully functional, was absolutely clean and was perfect for our family : 2 adults, 17y boy, 15 and 13y girls and mister little 7y. Certainly not large enough to live there permanently but really ideal for vacations. The building has got its own history (google Brunswick) and is quite surprisingly designed. The apartment is fully furbished with absolutely everything your need : kitchen is brand new and has got all required equipment. Worth mentioning that Mark kindly provided everything you need to clean the place, paper rolls for toilets, a few essentials like sugar/coffee ... very appreciable when you arrive in the place after a trip (although waitrose/tesco/sainsbury are really downstairs).
The Lady leaving next door will welcome you and give you the keys upon arrival whilst Mark will give you a virtual tour of the apartment over the phone explaining how things are working (incl. heating and WIFI). Departure I can't say (not departed yet) but I have no fear.
Mark was very responsive and replied to any text/mail within decent time-frame.
Overall ... very very nice stay !!!