function custom_format_checkbox_alt( $user_meta, $user_id ) {

    foreach( $user_meta as $key => $value ) {

        if( $key == 'boutique_awards_winner_2018' ) {

            if( empty( $value ) ) {
                $user_meta[$key] = 'No';
            } else {
                $user_meta[$key] = 'Yes';
            }

        }

    }

    return $user_meta;

}

add_filter( 'wpf_user_update', 'custom_format_checkbox_alt', 10, 2 );