It depends what build of (I'm assuming you use) Win 10 you have weather you can use Defender or not. Newer builds of Win 10 will automatically disable Defender if you install another AV solution. Microsoft even admits that Defender is only meant for users that don't have or don't want to use a good third-party AV anyways. I've never used Defender myself as it's not a robust AV compared to some free AV products even! This has been proven once again by 'recent' AV Comparatives testing.
Most of the major player's AV products are compatible with Immunet. Such as AVG, Avira, AVAST, Norton, McAfee, Trend Micro, Kaspersky & others. If you look at the Immunet's Exclusion list a number of AV's are already excluded by default. Personally I have Immunet paired with Panda Dome Pro.
It is a great idea if you use Immunet as a companion AV to create an exclusion/exception/allow rule for 'Immunet's entire Program Files folder' for the other AV. If the other AV you choose is not listed with Immunet's Exclusion list then also create a custom Exclusion rule for the other AV's entire Program Files folder as well.
This really can go a long way at avoiding possible future conflicts or problems between both AV's. They should recognize each other as safe programs.
Also, if you do use Immunet as a companion AV to another product it is recommended that you disable the ClamAV module & updates for it and just use the cloud engines instead. This will (sometimes significantly) decrease system resources being used by Immunet.
Best wishes, Ritchie...
P.S. - I'm not completely unfamiliar with Comodo. Back in the day I used just the Firewall & Defense+ modules minus the AV module enabled for some older builds of Windows.
I quit using Comodo back then because it was increasingly becoming a resource hog (bloatware).