WordPress registration extra field

// https://wordpress.stackexchange.com/questions/87261/checkboxes-in-registration-form


// REGISTRATION
add_action( 'register_form', 'signup_fields_wpse_87261' );
add_action( 'user_register', 'handle_signup_wpse_87261', 10, 2 );

// PROFILE
add_action( 'show_user_profile', 'user_field_wpse_87261' );
add_action( 'personal_options_update', 'save_profile_fields_87261' );

// USER EDIT
add_action( 'edit_user_profile', 'user_field_wpse_87261' );
add_action( 'edit_user_profile_update', 'save_profile_fields_87261' );

function signup_fields_wpse_87261() {
?>
    <label>
    	We will NOT use your contact details for any future marketing/promotional activities unless you consent and opt-in by ticking this box;<br />
        <input type="checkbox" name="consent_opt_in" id="consent_opt_in" /> 
        Opt-in?
    </label>
    <br />
    <br />
    <hr />
<?php
}

function handle_signup_wpse_87261( $user_id, $data = null ) {

    $feat_a = isset( $_POST['consent_opt_in'] ) ? $_POST['consent_opt_in'] : false;
    
    if ( $feat_a ) {
        add_user_meta( $user_id, 'consent_opt_in', $feat_a );
    }

}

function user_field_wpse_87261( $user ) {

    $feat_a = get_user_meta( $user->ID, 'consent_opt_in', true );
	?>
    <h3><?php _e('Marketing Consent'); ?></h3>

    <table class="form-table">
        <tr>
            <td>
                <label><?php 
                    printf(
                        '<input type="checkbox" name="consent_opt_in" id="consent_opt_in" %1$s />',
                        checked( $feat_a, 'on', false )
                    );
                    ?>
                    <span class="description"><?php _e('Opt-in to marketing material?'); ?></span>
                    </label>
            </td>
        </tr>
    </table>

	<?php 

}

function save_profile_fields_87261( $user_id ) {

    $feat_a = isset( $_POST['consent_opt_in'] ) ? $_POST['consent_opt_in'] : false;
    update_usermeta( $user_id, 'consent_opt_in', $feat_a );

}