I would stay well away from any Symantec products at all. If you can, uninstalling Norton Security (remember to follow the uninstall instructions, or you'll regret it) would be a very wise move. Macs aren't PCs.
Among those that have been providing tech support for a long time (in the neighborhood of 15-20 yrs or more) you will find the vast majority would never install the bloated mess that is today's Symantec or McAfee products on their own personal computer. I would find it highly unlikely anyone that has provided professional tech support for any length of time would personally use either of those products. There are also no gamers worth their salt nor any overclocker that would allow one of those on their computer.
Related to AdWareMedic, I would just about wager that even the author of this software does not have it installed on his primary computers - only on testbeds.
If you have already installed some piece of "adware" in OS X, then AdwareMedic is what you want.
If not, then it is not "required" to install any of these sort of things on your Mac under OS X.
What is required is for people to unlearn bad habits and learn safe computing.
If you use a computer in this day and age, you should not be an ignorant driver.
If my wife can go from my needing to wipe and reinstall the OS every 6-9 months due to the number of infections under Windows no matter what protection was installed to being adware/malware free with no protection installed using OS X for the last 7 years - anyone can learn to do it.
I suggest everyone understand, comprehend and implement safe computing habits. Don't know what those are?
Have a read through Thomas Reed's Malware Guide at The Safe Mac.
To keep abreast of current threats and vulnerabilities, his Tech News page.
Please note that a "vulnerability" does not equal a "threat".
About the only tool I would recommend if you want assistance in "safe browsing" would be the WOT (Web of Trust).