Every download starts with a full 14-day Pro trial, with no account and no card. After that it quietly becomes Free, and you can buy Pro whenever you want. Prices include tax where it applies.
The Windows installers aren't code-signed yet, so Windows greets them with a blue “Windows protected your PC” screen. That's expected: click More info, then Run anyway. It's the same app as the macOS build, from the same source. We'll buy a signing certificate once Windows demand covers the yearly cost; until then we'd rather ship it than make you wait.
One payment. No renewal, no expiry, no account. Free updates within the major version.