Moving to a new Mac

Install DiskDuo on the new Mac and sign in with the same account. DiskDuo runs on one Mac at a time, so it offers to move there, and the old Mac stops the next time it checks in. You can also free a Mac first, in Settings, under License.

Hiding your email from Apple

If you chose to hide your email, DiskDuo only ever sees Apple's relay address. Sign in with the same Apple ID on every Mac and it finds your purchase.

Refunds

Polar handles the payment and any refund. Once a refund goes through, DiskDuo stops working after it next checks in. Nothing on your Mac is changed.