I am also getting 'Security Certificate Not Trusted', in two different browsers.
Reluctant to proceed and sign up before we get confirmation from Mr Mangan directly.
Sean, I got the same thing (and others reported the same on FB), and I emailed Mangan directly to let him know. His response was "Oh don't worry it's fine." Nevertheless, I used the alternative method to sign up (sending an email response to the confirmation email instead of clicking through on the link) and it seems to have worked fine.