There may be some adjustment to UI needed to make this clearer, but the short answer is "Yes".
This is done conditionally: The module adds a checkbox saying "Create my site later" to the purchase form displayed on a product, if that product has the site feature. If that checbox is checked, then we go right to payment completion, and the client will create their site later using the regular aegir interface.
If that checkbox is not checked, we throw the user into a site creation form, store the data they input, and then use it on payment completion to create the site.
Regardless of whether or not they enter their site info during ordering, their client's quota is incremented.
In the case of a product kit with multiple sites included, only the first site can be created in this manner.