In simple terms, Heatseeker is effectively automated search find buy.
Whereas traditional SFB requires the visitor or buyer to manually go to Amazon, search a keyword, navigate to the appropriate search page, and click the product, Heatseeker instead provides a near-real-time direct link to the relevant search page with the appropriate keyword embedded and prompts the user to click the correct product.
Traditional SFB is notoriously problematic as it results in the visitor/buyer having to jump through hoops in order to get the product. And oftentimes, they'll skip the search step and instead search for <brand> <product> to find and buy the product. Heatseeker resolves this problem.