Commerce 1 get customer from user model
You shouldn't really need to do that, you're just adding custom fields to the user when those can be fetched easilly.
A customer will always be a user, but a user might not be a customer.

If you intend to get the customer details from a plugin (with PHP) you can just get the customer details (if exist) from the user, by using the Commerce_CustomersService

code example would be

$customer = craft()-&gt;commerce_customers-&gt;getCustomerByUserId($user-&gt;id);


this will either return the customer model or null (if a customer is not created against the user).