Most notably, the premium version of the plugin retrieves your product catalog from 1ShoppingCart and stores the data locally which reduces the communication between your site and the 1ShoppingCart servers.
The free plugin allows you to easily list your product on a page – similar to the screenshot below -
The paid version of the plugin allows you to list the products as you see above plus you are able to create single pages with product details too. A sample page of the product details page is below –
To see the paid version in action, go to http://wpdemo.equalserving.com/store/
The store page lists the “featured” products on one page as can be done using the free version. But if you click on the “More info” link under the Image Not Available image, you will see the product details page (http://wpdemo.equalserving.com/store/great-behavior-breakdown/) which can only be created using the paid version of the plugin.