I am setting up my sites, and have a domain multisite installation.
When I tried to change the section under Security/Hide Backend. This is supposed to set the login URL to xyz.com/login, xyz.com/admin, and xyz.com/register. That part worked.
But, when trying to go to a subsite, like 123.com (a sub-site for the multisite install where the 123.com site is domain mapped) then the redirect or pages did not work and when trying to login (the normal login page would show up), it wouldn't even find the page for the site once the user info was entered.
I have since unselected that to leave the login and registration pages as the default WP page URL's, but last time I did this, I was getting way too many false registrations and my site wasn't even running yet.