I/m not really seeing how this is different from the mod it is based off of. Could you please elaborate?

Sure.
The original mod is a chest with tremendous size (up to 2000 slots)
My warehouse only had a limited number of slots, but instead, when an item has over a stack of it inside, the excess is removed. When you pick from the warehouse, the amount is restacked to a full stack (provided you had previously added those items)
It works kind of like an infinity chest except that it is not cheat. The actual content of the warehouse is available using wires, as a hidden combinator tells you what is really in there.
The real reason is that when based are using large warehouses massively, the time out takes inserters (or loaders) to scan those slots becomes significative.
The mod updates the warehouses content over ticks, so that no matter how many warehouses you have, it will take the same computational power, however they will update less often.

That is a great description, I'd love to see it in the "information" page. Thanks!

Might also want to update the forum thread, since I was very confused when it was talking about something other than this specific mod.

instead of 100 items per tick, it is kinda useless when it comes to higher speed loaders, is that possible to increase the stack? like, right now it is always 100 inside.

Has anyone tested how much more UPS efficient this is compared to the original?

As long as it is 100 items/tick and not 100 items/sec that you can extract, I don't see a problem. However, I have not tried out the mod yet, so I might be wrong.

Has anyone tested how much more UPS efficient this is compared to the original?

As long as it is 100 items/tick and not 100 items/sec that you can extract, I don't see a problem. However, I have not tried out the mod yet, so I might be wrong.

I tested it against 1200 warehouses full of iron plates each with 2x6 loaders. vanilla I get 8 UPS, with the script, I get 42 UPS
That's quite biased as I update one WH per tick, so it takes 20 seconds between each update.

testing with mixed warehouses: 200 of 5 different items. Vanilla: 43 UPS, with mod: 40UPS
I knew I'd get negative profit on this test, but at least the overhead of the mod if not big
Loaders are miniloaders, aka inserters

Thanks for the reply. I intend to only use it with 1 item type anyway.

I am trying to decide between this mod and "Deep Storage Unit - DSU".

I will give this a try.