Can the app be used for paying in installments?

This can't yet be natively achieved with subscriptions in Shopify. Payment providers, such as ShopPay have these kind of installments integrated in their system. But overall, you could also just set the app to charge the customer every month and then delivery their product once every specific number of months. But you have to know that for each charge, Shopify will create a new order in your shop, which means that you will have to ignore it until the customer pays specific number of times.