We use flat pricing for volume discount app. There is no usage limit in both trial and paid subscriptions. Features and usages is not limited to store size or number of products.
Trial subscription: Every volume discount user starts with a 14 days free trail period. During the trial you will have full access to all the features of the app. There is no string attached, you can cancel the trial anytime you want.
Paid subscription: Once the trial has ended, your plan will be automatically moved to paid subscription. We use secured billing api of Shopify to manage our subscription and billing. You will be billed monthly.
Cancelation: If you want to cancel your subscription during trial or paid period, simply uninstall the app or contact our support.