From the file comments:
A module used for WonderPay's Preview Mode of redirected payment processing.
WonderPay offers a service that lets customers checkout on their secure server and can return completed order details to your website. This module interfaces with that by using a checkout pane to redirect the browser to an intermediate checkout page the displays the cart contents and creates the form to submit to WonderPay's service. Returned information is captured and turned into a new order, and at the same time it empties out the contents of the specified cart so customers can come back to your site just like they had checked out on your page.
As of right now, this module is not meant to be used in conjunction with any other payment method, since it bypasses the Ubercart checkout altogether.
Note that WonderPay offers an e-mail receipt service that you can turn off through your account. You may want to do this so you can leverage Ubercart's invoice e-mailing system instead.