This plugin has an impressive UI of its own. Where it falls down is how it integrates with WordPress's ordinary UI, and specifically the user profile page generated by WordPress. As @SamDecrock mentions, if you update the field for one user, it updates for all users, and the reason for this is because it tries to update the fields for the current user who is logged in making the change, as opposed to the user who is being edited. This can be seen on lines 897 and 1119 of plugin version 2.0.6. I have fixed this issue on my own site and can submit my code to the author if it is desired, but it's a simple fix.