To follow up on a previous response, I've put together a fairly large base (currently around 2k white spm, but it's still fairly unoptimized), and the mod has started to become pretty significant in it's UPS hit.
Here's what I've noticed during the setup of the base.
I currently am using it for just about every item in my base, so it's not terribly surprising that it's become noticeable, and this is likely an improvement on vanilla bots/trains/belts. On each refresh, the update takes around 220 ms, and has become a noticeable stutter every second. I have not changed the mod setting for the update period, so that's still at it's default. I could increase the value, but would need to check if throughput can be met - I'm using Schall's Machine scaling tier 3, so I have a dedicated quantum chest for input and output to most of these. In total, I'm at approximately 7500 quantum access points.
Currently, I also have the cap at 20k resources of each type, which I've increased a few times as the base grew. Originally, I used 2k as the cap (trying to minimize needing circuit conditions, particularly early game), but my copper wires were eventually bottlenecked. I assume this is because the quantum interface can only handle so many items per tick, so a 2k cap would effectively only allow me 2k x 60 = 120k items of a certain type/minute. Luckily, a max cap of 99,999 should allow enough throughput for most people: 99,999 x 60 = 6 million items/minute. For reference, my copper wires are at 1.7 million items/minute, so I might actually hit that.
For a personal UPS solution, I will probably try to move towards set-ups that reduce the quantity of quantum access points, but that will be a fairly major task. Schall machine scaling helped me out, because before when I was using a belt loader based setup, I certainly had more access points/assembler. Effectively at 2 quantum access/64 assemblers currently. However, I can't say for certain that it isn't purely the amount of resources being moved that's causing the impact. If you want Eliont, I would be more than happy to go over my world in more detail to see if there is any chance for improvement. It has been an extremely fun mod for a more casual playthrough, but still has some interesting logistical challenge in making sure you get the correct machines prioritized.