The huge takeaway for me was not the technology (or lack thereof). Ultimately all existing (and proposed) systems have flaws. The key was public trust in the result.
The first step to sidestepping democracy is to attack the legitimacy of elections. One can attack the process, software, hardware, ballot security, eligibility, and so on. It doesn't really matter what you attack - it doesn't matter if your gripe is legit or not. It only matters that you erode trust in the result.
If you can make people think the elections are rigged, then you can bypass them and move straight to authoritarianism.
Quibbling over open-source or not is irrelevant. We can cast doubt on the software either way. Quibbling over electronic or paper voting is equally irrelevant (there are plenty of paper-only elections worldwide that are very suspect.)
Naturally the Open Source company promotes Open Source voting machines. But in truth being Open Source has no (real) benefit. Software is easy to tweak, Open or not.