I did some testing and received some strange results:

https://imgur.com/a/IiI1gL4

The throughput seems to be capped at 120/sec as described in a previous post, but in some cases it can surpass that number.
Which begs the question, which is the correct number? Is it 120/sec or the described 270/sec?
The mod wasn't updated since the last response of the mod author, where he confirmed the cap of 120 items/sec, which leaves me confused.

Can someone explain what is going on?

Hi Kythblood, you are right I've been very inactive and not saying much. But as of 17.52 belts are no longer capped at 120 items/s. In my testing they can even exceed speeds of 270 items/s!! But at faster speeds the belts really start to randomly decompress themselves, especially around corners.

So I took a look at your testing. And you did find that the belts operate at their correct speeds. Like it is possible to get the speeds I've described for the mod. So why don't they work for some of your tests?? I don't think its the belts. I think it's the matter void. A single matter void will only void up to 120 items/s from a belt due to the way it was coded. I can't confirm that but I'm prettty sure that's the case. So when you use multiple splitters and matter voids, the belts work. The matter voids are the bottleneck. I bet if you test throughput, you'll find using 2 matter voids has a cap of 240 items/s. Let me know if that solves the problem, or if there really is some other issue going on

How did I not think about that. My bad.
I thought the matter voids simply delete everything coming in, but it seems they are capped like you said.

https://imgur.com/a/s6RGnZy

The only other issue I can think of, although really small and not directly mod related, is that Fast and Stack Inserters cant pick up items from a non compressed belt because they are too slow.

https://gfycat.com/insidiouscheerfulamericanpainthorse

Until now I simply changed the belt type each time so that it remains mostly compressed. I understand that this isn't an issue of the mod, but can you recommend a mod that adds faster insertions (not just more capacity) without adding a lot of other stuff?

Hey, is this still an issue (that the inserters can't pick items from the faster belts)?
I haven't tried the mod yet.

Inserters only really have trouble when the higher tiers of belts have a sparse amount of items on them. At least for fast & stack inserters. So it's really not such a big problem. I'm primarily using these for my main bus, and then using slower belts to branch off of it so naturally my inserters don't have any trouble. I made this mod so I can have a really really fast belt that feeds many slower belts where the inserters will pick from. But with that said, I do have some production lines being fed directly with these belts and haven't noticed inserters missing items being an issue.

Also, instead of looking for faster inserters (I don't have any mods I could recommend anyways), maybe go for loaders instead. Miniloaders is pretty great and adds nothing except the loaders as far as I'm aware.