Yep – I select that and it does use the users registered username and displays this at the bottom of the post.
What it doesn’t do use the name that the user has selected as their Public display nameIn their user profile.
In my case the username is their email address and their public display name is first last.
For the moment I’ve configured it so the user has to provide their name in the form, and this displays correctly in the post. Though this means all the posts are actually made by the same user – just the display name is different.
Cheers
Simon