Having a dual extruding machine, I see no benefit to a quad extruder myself, To be able to produce 4 x parts simultaneously and in a seamless flow, you are restricted to a very small area within each nozzle. You might have a 12" long platform, but the nozzles themselves to all rotate and print 4 identical items is very limited, it's no different on a dual extruder. You also need to precariously position the items to be duplicated so that the movements of each nozzle fall within eachothers boundaries.