My reply:

Fortinet must be pretty bad at maintaining site trust lists. They are likely flagging all .tk as malicious because when that extension came out, they allowed anyone to reg for 30 days for free, making it used by attackers a lot. This hasn't been the case for a very long time now. Most major vendors including WebSense doesn't have an issue with the domain. I can assure you that the site is not malicious.