As far as malware is concerned, if you are looking to protect yourself, then simply stay away from questionable app sources and don't click through messages that you don't recognize. While many of the security apps claim to prevent malware, mostly what they do is detect it after you've already got it.
That said, many of those apps do provide additional services like locating lost or stolen devices (although, it many jurisdictions, law enforcement isn't interested in tracking down a stolen phone or tablet... and you should never track it down yourself, if stolen.) They can offer backup solutions and other security to keep your data safe and private.
Personally, I've found them to be more of a hassle than anything else, but that's just my opinion.