You can make tests with paypal sandbox and it logs the ipn activity! So you can use your component as an administrator to see how many payments you have received.
Thank you so much for the encouraging review. I really appreciate it.
Based on your description though, I believe you meant to leave this review for the Nice PayPal Downloads extension and not the Nice PayPal Button plugin. As the Nice PayPal Downloads works with IPN and the Nice PayPal Button does not.
In any event, I simply wanted to say thank you and to clarify for the sake of other readers.
~ All the best