They're trying to expose IPC to the renderer in an unsafe way. See their discussion on this GH issue https://github.com/electron/electron/issues/21437 (referenced from the main readme as blocking some features they want to implement)
On their "building a secure app" page they complain about Electron's quick release cadence https://github.com/reZach/secure-electron-template/blob/mast...
> The trouble that I've found with electron, is that their release schedule is crazy, with only a few months before each major release. We know that electron is a young framework, but it is hard to keep up so quickly!
Electron releases quickly to pull in critical upstream security fixed from chromium. That reasoning is explained pretty thoroughly in the best practices documentation https://electronjs.org/docs/tutorial/security#17-use-a-curre...
I haven't looked at their implementations of the other security best practices, so these might be the only red flags, but I'd still recommend against just blindly copying the template without understanding and verifying the best practices they're attempting to implement.