Ethanol is not a very good motor fuel as it is not energy dense. Compared to gasoline ethanol has about 40% less energy by volume. This means fewer miles per gallon and less range on a tank of fuel. The synthetic ethanol would have to be very cheap to make the cost per mile comparable to using gasoline in a vehicle that gets 30-40 mpg.
What Joule Unlimited is producing is a drop in fuel. They can tune their bacteria to make any kind of fuel they want. The bacteria excrete the fuel and they skim it off. At that point its ready to go in the gas tank. No refining necessary. They don’t have to kill the bacteria. The bacteria just go right on excreting biodiesal, jetfuel, ethanol or whatever they have bioengineered the bacteria to produce.
I'd rather see the metric of fuel cost per each mile driven. Granted, this will vary from vehicle to vehicle, but match vehicle size/weight and just change out the fuel used, in order to generate the metric.