Yes, Personal Discount is free, up to 50 coupons generated per month.If you generate a coupon for your new newsletter subscribers, it means you can offer a discount to 50 of them per month.
No, it's a soft limit. The application will continue to work. We will notify you and give you some time to upgrade.
Due to some limitation in the Magento platform, you will be not able to see the expiration date of your coupons in your shop interface. You can however see the expiration dates in your Personal Discount dashboard. Personal Discount takes care of removing the expired coupons.
Running Personal Discount as a standalone app means that we can only interact with your store through an API. This is a more secure approach than installing a plugin that runs code on the same server where your shop is hosted. Plugins have direct access to files on the server and to your database, whereas the API access has a limited scope. For example, when you connect Personal Discount to your WooCommerce store then we ask only for write permissions so that our app can create coupons but not read your data - no access to your customers or orders. When you approve the API access then Personal Discount receives only an API key that we additionally encrypt before storing it in the database. Your login and password are invisible to us so we can't log in to your store admin panel. Another reason for favoring the API approach is that we wanted to avoid dealing with different versions of WordPress or WooCommerce. Connecting through the API is more stable and easier to maintain since API versions don't change that often. Hosting Personal Discount on our server has also the advantage that we can release changes, bug fixes or new features immediately to all our users, as opposed to asking them to update a plugin manually.