One of the bosses at Symantec (which makes Norton security products) recently stated that no security software can block more than 45% of the threats which are out there, so relying on
any security product to do everything for you is definitely unwise. (If you'd like some general tips on computer security, please take a look at my post at 17:51 here:
http://www.theanswerbank.co.uk/Technology/Computers/Question1351804.html ).
The stuff that most frequently gets through security systems is the sort of malware that (the free version of) Malwarebytes Anti-Malware seeks to get rid of, so I'd STRONGLY advise that you should have it on your computer. (NB: When installing it, take care to deselect the option to take a free trial of the 'Premium' version. When running it, don't be surprised if a scan takes ages to run; that's normal!)
Because (the free version of) Malwarebyes Anti-Malware is a 'run on demand' program, there's no risk of it conflicting with other security software, such as Comodo Anti-Virus. However, equally, because it doesn't 'run in the background' you need to remember that it will do absolutely nothing unless you actually ask it to do so. (i.e. you need to remember to run a scan every so often - once a fortnight is probably sufficient unless you're actually experiencing problems with pop-ups).
Some of the pop-ups that Malwarebytes seeks to get rid of are little more than irritations but others are the first step in a two-stage strategy to get you download something really nasty onto your computer. e.g. you get what appears to be a legitimate pop-up telling you that you need to update something like Java or Adobe Flash Player. If you click on the link you actually end up installing something like Cryptolocker:
http://www.bbc.co.uk/news/technology-25506020
So running Malwarebytes Anti-Malware occasionally (to ensure that you don't get any fake pop-ups in the first place) seems like a very good idea to me!