Important Plugin with great support
I have Wordfence Premium running on two commercial sites and the free version on a few other, non-critical sites. Both versions work great but what makes the Premium worth the price is the support and the little additional features that you can tweak for your particular requirements. I've only needed the support a couple of times, but when I have, they are there and 'on-it': Quick, knowledgeable, result focused and polite. All the characteristics you need when you are likely most vulnerable - under attack or threat of attack. If you run a commercial Wordpress site, Wordfence Premium is, in my opinion a must-have plugin.