|I currently do use Comodo DNS, and I can safely say that I trust it as another layer of security.|
The way that a DNS works is by translating what you type into the URL bar of your browser (i.e. http://www.computing.net) into something that servers understand, and IP address (i.e. 220.127.116.11) DNS servers have long lists of these name-to-IP address conversions, and you can specify to your browser which one to use.
Security minded people will often use certain DNS servers, because they implement useful features, such as blocking malicious IPs from being served. For example, let's say I type in www.thisisabadsite.com into my URL bar. A normal DNS server would see that, and return the IP 123.456.789.012. I would then be compromised by whatever exploit the site had. However, if I was using something like SecureDNS, it would see that www.thisisabadsite.com is a malicious website, and either return a warning, or simply tell my computer that site doesn't exist, effectively preventing the attack.
Now, I must warn you that these defenses aren't foolproof. New sites are popping up all the time, and DNS servers can't always keep up with the malicious ones. However, it is an extra layer of security for your computer that doesn't require a second though on your part once you implement it.
I hope I answered your question thoroughly!!