I've been using CIS 5 for over a year now and have not had 1 FP. My system is always clean and I use MBAM and HMP as second opinion scanners.
I use Sandboxie for my browsers and if I have to do something that is risky I open a virtual machine and save the current state as something so that I can revert back to it afterwards.
Technically, I don't think any antivirus software is even necessary if you use the Comodo firewall but the included AV doesn't get in the way and is just another layer of protection. Add Sandboxie for the browser(s) and use the Comodo sandbox
for unknown stuff that just pops up and lastly combine all that with a periodic MBAM scan and an AV software gets even less important.
From another angle, CIS has gotten so powerful and ridiculously easy to use that it just doesn't make sense to pay for security software anymore.