The best alternatives to StorePreviewer are SplitMetrics, AppMockUp, and Sketch to App Store. If these 3 options don't work for you, we've listed a few more alternatives below.
SplitMetrics replicates the app store experience and provides a detailed report on users on-page behavior. Think of your app store page as a landing page you can track and optimize. App Store metrics allow you to evaluate how effective your product page is by providing you with actionable data on app store users behavior.
AppMockUp is a platform where mobile app developers can create the most compelling screenshots for the App Store and Play Store. It's fast, easy and free.