Thank you for your detailed feedback!
I'm glad you appreciate the lack of word limits in Multi Find.
I'm continuously working on improving the extension, and your input is invaluable.
I'm aware of the slowdown issue with many words (and long webpages) and am exploring ways to optimize performance (v1.81 should already be faster than v1.80, and you can try to set diacritic sensitiveness *on* to speed up even more).
The reason why there are no different settings per site is that the extension is not aware of the navigation URL, for confidentiality issue. There is for now no plan to change that but the different word lists are on my radar instead. I hope to add this feature in a future update. Thanks for your support and patience!