Back when I had Windows machines I used Webroot's products for awhile. I thought the software was solid and it never gave me any issues. Having said that, I don't use this or any other security suite software on my Mac. Now, if you send files back and forth with Windows users and want to help protect them, then I could see installing it (although I still wouldn't).
I use Webroot Secure Anywhere on all my mac's. Just a little extra piece of mind. Doesn't hurt and runs really light. If you don't want it send me the code private message and I will gladly use it. LOL