For any version of Dragonfly installer (Windows) that you have downloaded or got from a colleague, you can execute it to install Dragonfly and immediately get a free 30-day trial with full features without need of a license key to activate it. This 30 day free trial is only available once for each computer, so you can't get another 30 days by uninstalling and reinstalling, no matter what versions you reinstall.
When your trial expires, you need a license key to activate Dragonfly to continue using it. It could be either a perpetual general-purpose license or an annual non-commercial license.
For Linux users, the first installation doesn't provide you a free 30-day trial. You need a trial license to activate it.