It is generally recommended not to, but noone actually tried it recently, so it is somewhat an urban myth. IE is considered unsafe because of IE6 history, though we have IE12 already. AVs have evolved as well and Windows 10 can handle a lot more than XP. People have been running multiple AVs for years and it was even recommended by security experts, they were called antivirus, antispyware or etc back then, but basically all were AVs. Eventually they merged into one product, so obviously, no company would advice people to run a competition software alongside of theirs. Though some AVs states, that you can run them alongside of other AV. Some computers can not even handle a single AV (BSOD, sluggishness), it all comes down to quality of a specific product. The best way to find out, is to try it out yourself. The worst scenario would be an unbootable Windows, the best case scenario, an increased protection at the cost of some system resources of course, so as long as you have a system imaging, there is no harm in trying. You could make it work better for example by using a realtime protection in one and using a web protection in other one.