I sent a tweet to the Genuitec Twitter account about the problem, and they asked me to post about it here (even though it’s an issue with the Genuitec website and not the GapDebug product).
The beta signup works fine in Chrome, but not in Firefox 29 (on Windows; doubt that’s relevant). In Firefox 29, with Firebug open, I can see an error occurs on the POST but the page redirect happens too fast to catch the details. There’s no visual feedback on the page itself to indicate that the signup failed, other than the fact that there’s no feedback indicating success either.