Nope; I love the feature (it plays in sync for me!), but I am also struggling to turn it off! I went into the Alexa app on my phone and chose to play back only on one device, and that worked, but when I later asked my living room Echo to play, they all started back up again.
(I thought there might be a workaround in creating a "group" with a single Echo in it, but an echo can only be in one group at once, so I can't have, say, my living room Echo in both the group "Everywhere" and the group "Living room"...)
Until there's some instructions for the thing available I've deleted the multi-room group I created and things have gone back to how they were.