Comments on alternative to user sync

I am really trying to get to the bottom of this. The warnings I am getting from the plugin while in debug make me a little uneasy, so I was looking at other methods.

On the wordpress site they have custom_user_tables described as an option. here is the content from the wordpress site:

Custom User and Usermeta Tables
CUSTOM_USER_TABLE and CUSTOM_USER_META_TABLE are used to designate that the user and usermeta tables normally utilized by WordPress are not used, instead these values/tables are used to store your user information.

define( 'CUSTOM_USER_TABLE', $table_prefix.'my_users' );
define( 'CUSTOM_USER_META_TABLE', $table_prefix.'my_usermeta' );
Please note that permissions in the user_meta tables are stored with the table prefix of the site. So in the CUSTOM_USER_META_TABLE one must have entries for each site using that table. At the very least for the administrator, to avoid the "you do not have permissions error" you should have:

prefix1_capabilities = a:1:{s:13:"administrator";b:1;} and prefix2_capabilities = a:1:{s:13:"administrator";b:1;} etc

When using CUSTOM_USER_TABLE during initial setup it is easiest to: Setup your first instance of wordpress. The define statements of the wp-config.php on the first instance pointing to where you currently store user data wp_user by default, and then coping that working wp-config.php to your next instance which will only require you to change the $table_prefix = variable as previously stated. At this point the install will run as expected; however, do not use an e-mail address that is already in use by your original install. Use a different e-mail address. Once you have finished the setup process log in with the auto generated admin account and password. Then promote your normal account to the administrator level. Log out of admin. Log in as yourself. Delete the admin account and promote the other user accounts as is needed.

I am not sure how this would work when the wordpress install and related tables are on completely different servers/domains, though.