For starters, cost. Now you have to buy two machines for every single machine you buy. It also means taking up more room. Now, instead of fitting 10 machines in a single space, you can only fit 5, creating even longer lines. This also increase the chances of failures. A single machine failing means both machines in the pair fail. So, you've gone from 10 machines to 5 pairs of machines for twice the cost. You guy from a single machine putting you down to 90% original capacity (assuming 10 machines) where as a single machine brings you down to 80% capacity (40% of original capacity).

Not to mention the additional level of confusion and potential for errors. All of this so you can buy two machines from two different vendors who might, in the end, still have ties via investors.

Some suggest each party should have a set of machines, so that the interest tension would cancel errors a lot.

Where I voted (Massachusetts) you voted with a paper ballot, then watched a poll worker feed it into a machine which recorded it.

Too logical ;)

this with some crypto-sauce would be mixnet voting :)