It's hard to tell quite what audience the Muffin Man seeks to serve, but it seemed popular with ladies of a certain age and youngish people who were dressed very tidily. Chairs were wooden, and pictures of old London were popular. Service was not really with a smile but not with a frown either, and it was a pleasant enough place to be. Much better than a Costa.
For less information, see http://themuffinmankensington.co.uk/