My husband and I had a great week at the Nell Gwynn flat. It had everything we needed and was located in a great area for walking to everything we wanted to see in London - Buckingham Palace area, many museums, Hyde Park, Kensington Palace, Westminster Cathedral, and Paddington train station. It felt safe to have the lobby and front desk attendant and they were helpful for giving information and getting us cabs, etc. All was clean and modern.
Our only complaints would be that it looks much bigger on its online site, but big enough and likely still a good deal in the center of London. The bed is listed as both “king” and “queen” size in its listing, but it was closer to a full bed in the US - definitely not anywhere near king. Without air conditioning we needed to keep windows open all night and we were comfortable, but there were some nights with loud neighbors we could hear til very late. Perhaps this is normal for Europe, but the only coffee maker was a French press and a hot water heater.
All and all this was a great week!