The description says:

Might be computationally expensive in large factories (see FAQ for more details on performance)

Unfortunately, I can't find the FAQ.

I've tried the mod my Space Exploration game, and exactly every 60 seconds, Factory Inspector will jump from about 0.1ms to 10ms script update time, which unfortunately tanks my UPS for a few seconds from ~60 to ~30 :(

Could you send me your base please?

And my apologies, the FAQ never got written. I'll write up the current approach to performance management, but there's definitely still work to be done here. Ultimately what the mod is trying to do is pretty difficult and I haven't found a faster way yet.

I agree, it is difficult indeed. This is why I used a startable job in my Usage Detector mod, instead of continuously reading everything.

I think you can save some computational power by delaying as much computation as you can. I read your "design" text file and saw that you do a lot of calculations when the UI is not open. Only calculate the pure numbers when the UI is not open, and then do the detailed calculations (amount_crafted + per second) when the UI opens. This alone is by far not enough to improve the performance enough, but it is something...