So I was wondering if there is really any advantage to having a universal coin mechanism over a metal guide that the coins just fall through?
There is no advantage to buying a universal coin mech, unless you are trying to prevent certain types of slugs, metal objects, or other stuff from registering credits. If your main purpose is to drop something (anything) into the slot and get credits, you have solved the problem

Coin mechs only prevent slugs, and other junk from getting credits. But yours should work fine now with anything, as long as in hits the switch at the bottom.