The new version can set any inserters stack size via the circuit network by using integer overflow. It works with normal inserters and with filter inserters in "set filters" mode. There is no downside and it will not influence anything (like slowing down the belt) but the stack size. It is not limited to a stack size of 1 like the old version and it uses just one constant combinator instead of nine combinators. Unfortunately this does not work when taking from a chest.
The gif first shows the left inserter with its stack size set to 1 and the right inserter with its stack size set to 2 and filter set to iron plates. In the second part of the gif the left inserter stack size is set to 5 and the right inserter stack size to 1. The nixie tube displays how many items are in the corresponding chest.
It works like this:
The combinator value, let's call it X, is calculated like this:
X = 2147483648 - desired_stacksize
* stack size 1 has combinator value 2147483647
* stack size 2 has combinator value 2147483646
* stack size 3 has combinator value 2147483645
* stack size 11 has combinator value 2147483637
* stack size 12 (max) needs no combinator..
There is one thing to note. You may only connect one wire type, either red or green, but not both. If you connect both, you need to use this formula:
X = 2147483648 - 2 * desired_stacksize
That is because each wire type will reflect back the hold value to the inserter. Two wire types reflect it twice.
Here's the old post: