Really great mod. However, it's impossible to find it due to its weird naming, I only found it by accident really. I would suggest putting "inserter" keyword in the name. Maybe "UPS friendly inserter box" or something like that :).

I'm using it with merged chests mod for UPS friendly factory, and it's working mostly great. There is one disadvantage though. Unless assembler source item requirements are whole numbers (integers), you really need to oversaturate your sources. The worst is if assembler needs like 3.12 iron per second, which is close to 3, but you have to set the stack size to closest higher integer which is 4. But then instead of 187.2 iron per minute, you need to oversaturate to at least 240 iron per minute, which is a lot (otherwise other assemblers will starve, because all optimizers take the source items on the same tick). You can of course design a circuit network to drive the stack size, but it becomes cumbersome.

Perhaps it would help a little, to not overfill the machine slots, but only put in few source items into assembler, like inserters are doing. Or loaders - for example in the mod "Loaders modernized", you can choose for each loader to "overfill the machine slots" or not.

Another option would be a possibility to skip some transfer intervals. Like the yellow optimizer is capable of 1 transfer per second, but a possibility to set it to only 1 transfer each 3 seconds.

Yes, I realise the title is misleading, but once it’s been uploaded, it’s no longer possible to change the mod’s name. That was a mistake on my part.

But going back to the calculations, the mod was originally created solely for moving items from one crate to another or from one warehouse to another.
Adding the option to load buildings or unload trains is a bit of a bonus – because I reckon this mod is quite overpowered.
So, as you say, it’s best to control it via a network and programme it exactly as required – perhaps in collaboration with another mod of mine, ‘Pythonator’, it would be easier.

And thank you very much for the feedback.

Quick correction to my previous reply: the internal mod name can't be changed, but the displayed title can. I've renamed it to "Storage Optimizer – UPS-friendly stack inserter & loader" and updated the summary, so it should be easier to find now. Thanks for the push!

About loading machines – you're right, and here's what actually happens: when the target is an assembler, the optimizer keeps filling its input slot until it holds a full stack (e.g. 100 iron plates), unlike an inserter, which stops at roughly two crafts' worth. So at the start every machine pulls far more than it consumes, and the machines further down the line starve until the first ones are full. Once they are full, each machine only takes what it actually uses – so in the long run you don't need 240/min, the extra supply is only needed to fill those buffers.

Workaround for now, no other mods needed: connect the assembler to the optimizer with a wire, set the assembler to Read contents, and set the optimizer's enable condition to e.g. Iron plate < 10. The machine then keeps just a small buffer, like with inserters.

An option like "don't overfill machines" is on my list of ideas, but I want to think it through before adding more settings. Thanks again for the detailed feedback!

Thank you for changing the name (description). Now I found it immediately just searching "inserter+UPS"! I reckon you will get much more downloads from now on. Yes yes, you are right, once assemblers are full, the integer issues goes away, but, takes a long time to fill them up :). With additional circuit of course everything goes. For now I'm just combining your storage optimizer with classic inserters here and there, cause it's so time consuming to circuit around so much. Your Pythonator looks interesting. Will have a look.