Can I offer a subscription box functionality with your app?
Yes, you can. Seal Subscriptions app has an integration with Bundler - Product Bundles app (https://apps.shopify.com/bundler-product-bundles), which gives you the functionality to offer subscription boxes to your customers.
In Bundler, you just create a Mix & Match bundle, which allows customers to combine products and in Seal Subscriptions app, you create a subscription rule for these products. Your customers will be able to build their own subscription box and subscribe on all products added to the box at the same time.