This mod adds an additional five tiers of belts to the game, beyond what is currently available from other mods. The fastest belt in this mod is equivalent to 6 express belts.
Simple as title is.
The splitters seem to not be able to handle full belt throughput of the same level belt.
you can see here the image proof https://ibb.co/7jSVQn1
It's stacking up at the input end and it's starving at the output end.