Why it's short, and what you get.
The trial is Unlimited — every checker, every integration, the full dashboard. It runs for 3 days by design: long enough to evaluate on real traffic, short enough that a competitor can't quietly map the whole product surface.
It's one trial per server and one per email address: re-registering with a new email on the same machine won't reset the clock, and re-using an address won't issue a second trial. Upgrade any time from the cabinet — your instance keeps running without reinstall.
If someone gifted you a license before you signed up, that's what you get on registration — the paid time you were given, rather than a trial stacked on top of it.