I know this isn't exactly the same as PHPUnit or Behat, but you're going to have a difficult time convincing developers to move away from those.
No developer is going to convert an existing PHPUnit test suite to this, but some information on the page about why I should use this instead of (addition to?) PHPUnit on my next project would be great.
PHPUnit is an awesome tool (I even started https://github.com/brianium/paratest to get a little more out of it). Behat is equally awesome.
However we wanted something that was a little easier to extend, in a variety of ways. We spend a lot of time writing JavaScript tests with Mocha and Jasmine for JS apps that consume our PHP APIs, and we really enjoy that style of testing.
This is our way of bringing that style to PHP, and we think its a great tool for new codebases.
Thanks again for the comment :)