Wordpress Multisite + Groups Plugin: Check if user is in group

gistfile1.php

<?php

	$blog_id = 1; //set the blog id to the main site id 

	switch_to_blog( $blog_id );

	$user_id = get_current_user_id();
	$group = Groups_Group::read_by_name( 'Premium' );
	if ( Groups_User_Group::read( $user_id, $group->group_id ) ) { 
		echo 'Premium';
	} else {
		echo 'Not premium';
	}

	restore_current_blog();

?>