(Just for the record for anyone reading) When this feature is active with default permissions the unregistered see a text box at the bottom of a thread. There is nothing there to indicate they still must register for their post to be published. Then after they compose their post and hit "submit," they get this:I will test this feature when I am on 2.2. So, I can't speak from experience yet.
If I were to use this I would put a phrase in, explaining the feature, inside the text box (Where by default it says "Write your reply"). To let them know they still need to register for their post to be published.