What do you learn about me when I pay?

Less than you might expect. Checkout runs through Paddle, the merchant of record: your name, card number, and billing address go to Paddle for payment and tax purposes and never touch our servers.

What reaches us is a confirmation that the public key of your account is now Pro, plus the order amount. The billing relationship, including the receipt email you enter at checkout, stays with Paddle. So a phrase-only account remains pseudonymous to us even as a paying customer: we know that you paid, not who you are.