Most important for me is being able to simply read the ballot and research candidates at my leisure. Not sure about failure points, my state has used mail voting for many years without issue and if Trump’s lackey makes ballots go missing I will know because I can track my ballot on the state’s website.

A really important point is some voting machines are ‘ballot marking devices’ which give you a human readable paper ballot with your choices (good) however the actual counting is done using a barcode or QR code (bad). There is never a good reason to prevent voters from verifying their ballot has their intended choices, yet some areas still insist on using these absurd machines.