Checkboxes in registration form

Short of creating a custom registration page, there are not much hooks that can be used to add custom fields to the default form. I tried once (with register_form hook) and only default fields (description, website, etc) were successfully recognized and saved.

Found this Q&A that has a workaround: Adding extra info via GET while registeration in wordpress

Here’s a proof of concept:

// 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>
        <input type="checkbox" name="custom_feature_a" id="custom_feature_a" /> 
        Enable feature A?
    </label>
    <br />
    <label>
        <input type="checkbox" name="custom_feature_b" id="custom_feature_b" /> 
        Enable feature B?
    </label>
    <hr />
<?php
}

function handle_signup_wpse_87261( $user_id, $data = null ) 
{
    $feat_a = isset( $_POST['custom_feature_a'] ) ? $_POST['custom_feature_a'] : false;
    $feat_b = isset( $_POST['custom_feature_b'] ) ? $_POST['custom_feature_b'] : false;
    if ( $feat_a ) 
    {
        add_user_meta( $user_id, 'custom_feature_a', $feat_a );
    }
    if ( $feat_b ) 
    {
        add_user_meta( $user_id, 'custom_feature_b', $feat_b );
    }
}

function user_field_wpse_87261( $user ) 
{
    $feat_a = get_user_meta( $user->ID, 'custom_feature_a', true );
    $feat_b = get_user_meta( $user->ID, 'custom_feature_b', true );
?>
    <h3><?php _e('Custom Fields'); ?></h3>
    <table class="form-table">
        <tr>
            <td>
                <label><?php 
                    printf(
                        '<input type="checkbox" name="custom_feature_a" id="custom_feature_a" %1$s />',
                        checked( $feat_a, 'on', false )
                    );
                    ?>
                    <span class="description"><?php _e('Custom Feature A?'); ?></span>
                    </label>
            </td>
        </tr>
        <tr>
            <td>
                <label><?php 
                    printf(
                        '<input type="checkbox" name="custom_feature_b" id="custom_feature_b" %1$s />',
                        checked( $feat_b, 'on', false )
                    );
                    ?>
                    <span class="description"><?php _e('Custom Feature B?'); ?></span>
                    </label>
            </td>
        </tr>
    </table>
<?php 
}

function save_profile_fields_87261( $user_id ) 
{
    $feat_a = isset( $_POST['custom_feature_a'] ) ? $_POST['custom_feature_a'] : false;
    $feat_b = isset( $_POST['custom_feature_b'] ) ? $_POST['custom_feature_b'] : false;
    update_usermeta( $user_id, 'custom_feature_a', $feat_a );
    update_usermeta( $user_id, 'custom_feature_b', $feat_b );
}