I have used a number of extensions, some good some not so good. I watched the video on you tube about using and setting up Web Optimizer using this plugin, and was sold.
I purchased the Pro version of this plugin, and it was definitely worth the money. It has made life simpler and Mike has helped me design my first test, including giving me guidance on setting up alternatives to allow me to test my existing site.
Experienced a problem, and after a few back and forth exchanges, the problem was resolved and promptly issued a patch.
So in short, great plugin, excellent support and help that goes beyond.