ThreatFire compliments your existing security tools which react to an infection only when the vendors knows about it and updates the signature while Threatfire constantly looks for malicious activities rather than a set signature pattern. 
This chart on ThreatFire website shows the effect it has on your system when combined with the exitsting antivirus software. An other way to look at is what you are missing on the Security front which you hope you are covered.
Features of ThreatFire include,
Persistent zero-day threat protection made easy for everyone
Displays detailed data on all running processes and allows you to terminate any process on demand.
Malware quarantine and removal, rootkit scanner, advanced custom rules settings and more!
Patent-pending ActiveDefense technology intelligently scans and analyzes computer processes to detect and block any malicious activity – without false positives!
Runs in background without impacting system performance.
Highest level of out-of-the-box accuracy. No need to configure baffling, technical security settings: just turn ThreatFire on and start blocking malware.
Perpetually ready for the next malware outbreak – detects malware by watching for malicious behaviors.
Enhanced user interface elements provide more technical details on alerts and interactive reports in ThreatFire’s main control panel.
Automatic updates run silently in the background so ThreatFire is always up-to-date.
Protects againstviruses, worms, trojans, spyware, keyloggers, buffer overflows, and rootkits- even if the threats are brand new and have never been seen before.
Works alongside your other security programs – in most cases you can use ThreatFire with your other antivirus, anti-spyware, firewall or other security programs.
Click here to download ThreatFire for your PC or laptop.ThreatFire works on Windows 7, Windows Vista, Windows XP and Windows Server 2003.