We try to combine the best of both worlds: a WordPress plug-in on the "client" side that the user can, for instance, install to define the tests, see the graphics with the results, or consolidate the winning alternative, without leaving the WordPress environment (meaning there is no need to learn a new tool), plus an external back-end that takes care of recording and processing all the relevant data to evaluate the performance of the tested alternatives.
This has advantages both at the technical and business level. On the technical side we lift all the processing load from your own server so that the tests do not slow down your site or interfere with your hosting provider limits. On the business side, because this gives you the option to try the service without paying a full plug-in license upfront and guarantees that you’ll always have the latest version of the plugin / service available, instead of just being covered for a given period of time.
Moreover, an ongoing relationship will help us to provide a better service. Thus, for instance, we may advising you on your best testing strategy based on what you have attempted so far, propose new tests, help you understand the results you get, and so on.
Don't forget that A/B Testing is only the means to an end (optimize your conversions) and not the end itself. Our mission is to make sure you bring your site to the next level, not just to provide you with a tool to do all the work on your own (unless this is what you prefer, of course).
Check also Five reasons why WordPress services are better than commercial plugins for a more elaborated (and generic) answer to this question.