You download the software, click "Activate trial," and a clock starts ticking down from 14 days. By the time you’ve finished setting up your email filters, the trial is already sending you passive-aggressive pop-ups asking for your credit card.
Once your 90 days are up, you cannot simply reinstall Windows or use a new email address to get another 90 days. Bitdefender tracks your hardware ID. You will get a message saying, "This trial period has already been used on this device."
There is zero risk. You aren't entering a credit card. You aren't signing a contract. You are getting three months of a top-three-in-the-world antivirus suite for exactly $0.