I'm reasonably confidant that 5 arms is the minimum without a massive increase in cycles, and that bottlenecked as it is by the single salt input, the cycles are at a minimum as well. Maybe there is something overall better that is slower but with fewer arms, but with the 13 different output locations, I doubt it. I'm less sure about area with all the space the tri-arm takes up, but I just can't see how to quickly handle the waste with only a single arm otherwise.