There are 2 extensions under extension of Adobe Launch and developer often gets confuse which to use when and what is the difference.

Below are the major differences between the 2 product string extensions in launch

• Adobe Analytics Product String:
  • Works accurately when the product data layer is not in an array format
  • A data layer with variables for all product related data (i.e. product ID, quantity, price, merchandising eVars, and currency events) is required
  • Can only associate an event with the product string. No way to automatically set up merchandising variables
  • Not the recommended extension for Product String
  • URL : https://experienceleague.adobe.com/docs/experience-platform/tags/extensions/adobe/product-string/overview.html
  • It is developed by Adobe Consulting
• AA Product String Builder
  • Works for product data layer with an array format -> Just provide the path before the array initiated in the collection path field
  • Can set up automated events and merchandising variables associated with the product string in this extension
  • The AA Product String Builder provides the ability to create product strings representing everything from the simplest Product Viewed event to the most complex Order Placed scenarios
  • The AA Product String Builder automatically manages s.events for custom events set within the product string. It also respects events set by the Adobe Analytics extension
  • Multiple AA Product String Set Variables actions may be used in the same rule
  • Recommended extension
  • URL https://techdocs.searchdiscovery.com/adobe-solutions/adobe-launch/launch-extensions/aa-product-string-builder
  • It is developed by Search Discovery

If you want to use the custom code option then check Product String in Adobe Launch