Using this, it is very easy to set up a smart furnace which can smelt copper/iron as well as stone bricks and steel. Also could smelt more if they would add ores or you would build this in modded.
By using negative values, we can enable the filters if x amount of an item is in the chest. This way, we can make sure that the inserter to the furnace does not take the iron plates, unless there are five in the chest and does not take the stone ore unless there are two.
You need to have all the inserter upgrades otherwise it will not take five at once.
Of course that is easy to fix by triggering the inserter twice if iron = 5!
Feel free to checkout the video in which I showcase the design (starts at: 17:21):
What do you guys think - seems like a pretty neat design to me!?