There are two things that I think you really need to do:

  1. specify the currency that the purchase will be made in - Australia, and several other countries, also use the dollar. At present it is extremely misleading. I expected a charge of $20 (Australian dollars; after Pi Day discount), and instead I have been charged $26.09 and an international conversion/transaction fee.
  2. specify what operating systems are supported. Presently, this seems to only be shown beside the third Download link at http://www.manuscriptsapp.com/, near the very bottom of the page. You should (a) detect OS and deliver an appropriate warning if it's not Mac OSX, or (b) make the system requirements very clear on the purchase page.

I now have a piece of software that I can't use.