Getting a user custom field value is contingent on knowing the custom field "key" (the name with which a value is stored under -- e.g. a custom field name/key of "favorite_color" may have the value of "blue"). You probably know that.
I'm not familiar with Magic Members and since it is a commercial plugin I can't investigate it for you. The first thing I would have checked would be to see if the extra custom user fields are indeed being stored as traditional WP user custom fields. It's possible the plugin is storing those extra fields in a different way (as a plugin setting or in a separate data table).
If it does use the WP user custom fields table, then it's just a matter of knowing the exact custom field names/keys it uses. As a commercial plugin, you may be able to request that information from their support team.
If you have access (and the comfort level) to view the database tables for your site, look at the table that ends with "_usermeta". The "meta_key" column contains the names you need to know in order to use the plugin's widget, shortcode, or template function to access the associated "meta_value". So find the "meta_value" that contains information you supplied Magic Members via the User profile page. If it's there, then the associated "meta_key" is what you'll use with Get User Custom Field Values.
Hope that helps!