They are 2 different programs. BOClean is an anti malware scanner and Threatfire is a behavior blocker like Comodo's HIPS. If your using Comodo firewall you do not need Threatfire. I myself do not trust anything made by PC Tools.
+1.
Comodo BOClean= Antimalware App.
Threat Fire= HIPS.
With Defense+ in CFP 3 you DON'T need Threat Fire. Defense+ is MUCH more powerful HIPS then TF.
Josh