The concept is good, but the difficulty is very high. Upon further experimentation, it appears that something that contributes a large amount to the difficulty is the way splitters work. My expectation was that they'd split the item stream evenly between items: i.e. send an item in direction 1, then send the next to direction 2, then the one after that to direction 3, assuming the input can be accepted by all directions. Instead, the splitter appears to simply use directions 2 and 3 as overflow in the event that direction 1 cannot receive the item. This makes it very hard to make sure that you're getting, for exmaple, both stone and brick, or converting the right amount of iron into the components while also maintaining enough raw iron, etc., without a lot of micromanagement.