I like that it's easy to use even if you're not familiar with A/B testing or analytics tools in general.
It also has some nice features that make analyzing results easier than other services we've used previously (such as Google Analytics). We are using this tool only internally at our agency but have been able to see how effective different methods of content delivery can be through its platform. The biggest challenge right now would probably be figuring out where to go next when an experiment doesn't seem to work well enough.