What purpose does the m-unit serve?

Electrical is not my strong suit, so I'm looking for an explanation. I have a 71 CB350, with a new stock wiring harness. I'd like to replace the stock handlebar switches with the Motogadgets pushbuttons, and every site seems to point me towards buying a whole MG system ($600). But I'm not sure if I understand the value in the m-unit (blue or otherwise) in my situation.​Edited to move this - didn't realize there are two almost identical subs for caferacer(s) via /r/CafeRacers https://www.reddit.com/r/CafeRacers/comments/aion6l/what_purpose_does_the_munit_serve/?utm_source=ifttt