Windows Ameliorated does not require installing from an ISO. That was merely made for convenience, and for those without the basic technical knowledge required to perform a manual amelioration. There is detailed documentation for performing a manual amelioration, it uses fully open-source scripts.(https://wiki.ameliorated.info/doku.php?id=documentation_21h1)

The ISO has been used by hundreds of people, with no sign of malicious intent, so personally I'm willing to trust that as well.