How do I allow other admins to see and use WPMU DEV?

I'm having difficulty with allowing my other site admins use of WPMU DEV. I've added the following code to wp-config.php:

define('WPMUDEV_LIMIT_TO_USER','1,2,3');

Now in the "Manage" tab I am seeing the message, "Only the admin users "User1", "User2", "User3" have access to the WPMU DEV Dashboard plugin and features on this site." However, the other users still can't access the plugin on the dashboard.

Have I missed something?