What do you audit if both the tally and the paper ballot are consistent? The only check possible is the voter checking themselves before they hand over the paper ballot.
My preferred machine would be one that did not use integrated circuits, but was simple enough that the entire board and circuit was visible - with no software beyond the circuitry at all. You just need a very simple sensor and tally wheels that mechanically advance, like those used for measuring wheels etc. No need for memory. Keep automation to the absolute bare minimum.