query usermeta from custom field

I haven’t touched user functions so far, but according to the codex, should look something like this.

 $args = array(
      'meta_key' => 'g300',
      'meta_value' => ','
 );

 $users = get_users( $args );

EDIT

This assumes that all the users with the field unchecked have a comma value ( for example, it won’t work if the value in the DB is empty ).

Example 2

 $args = array(
      'meta_key' => 'g300',
      'meta_value' => 'I will attend the G300 class,' //Was the comma intentional? If not, remove
 );

 $users = get_users( $args );

 if( !empty( $users ) )
 {
      foreach( $users as $user )
      {
           echo $user->display_name; //name
           echo $user->user_email; //email

           $meta = get_user_meta( $user->ID, 'is_700_a', TRUE );

           echo $meta; //the meta field value
      }
 }