Not only will alternate recipes break this logic, you need to set the production before it will even input any items, so it doesn't just magically know what's on the belt until you set it for a recipe and then it scans the input to make sure it receives the right item. Not to mention that would only work for ore, limestone and copper ingots. There are 2 normal and many alternates that use iron ingots, not to mention the steel alternate uses iron ingot, not raw iron, Iron rods are used in about 3 different recipes, iron plates in at least 2 that I can think of, plus 1 alternate.... etc.
So you would have to be exceedingly lucky to not have to make an extra click to set the recipe you want. if it auto set iron bars and you wanted plates you would then have to click back to the recipe page, then set the one you want, as is it automatically starts on that page unless you have already set it.