Marc's annex was very spacious, comfortable and located with convenient links to public transport. We stayed for one night when we traveled in to London, and then out to the Warner Bros. Studios Tour so the annex was superbly located. The door had an access code to get in so checking in was a breeze as Marc told us the code beforehand.
The annex itself was actually much bigger than we expected, and the bed was very comfy. There were lots of little touches around the room, from a board of locations where previous guests could mark where they had been, down to a choice of coffees and breakfast options.
I can wholeheartedly recommend the annex to anyone staying in London.