The trick with these fancy e2e-verifiable schemes is that they're very good at providing the voter with evidence that everything worked perfectly, but if something goes wrong, and there are a lot of ways for things to go wrong, it's not necessarily easy to pinpoint the problem.

ElectionGuard happens to be open source, but that's not a requirement for security. In fact, the magic of e2e-verifiable schemes is that they create a much more interesting property called software independence, which means that we can verify a correct election outcome without being required to trust any of the software used by the election officials.

Risk limiting audits, by the way, are also a method of achieving software independence, without any cryptography at all.