The tradeoff here is that you'll only get the default "GETRESPONSE" intent, meaning you can only have a single response mocked out at a time, but we figure that's a good starting point for a lot of people. And you can always switch to the older (and more advanced) setup anytime you want to take advantage of the full set of features.
To get onboard, all you have to do is follow our beta testing self-registration link here. That'll take you to the Alexa skill store, and you should see a modal like this:
With setup being so easy, we plan to release a series of articles in the coming weeks about all the stuff you can do with Responder, so be on the lookout.