Re: "My keychain has 2 sizes each ..."
I think the decent sized Leatherman's blades are a bit over 3". But then it doesn't exactly have a butterfly knife's speed of deployment. Might be faster to shove the pliers up a miscreant's nostrils and give them a good twist rather than try getting the blade out.
But the only time I've ever been stopped while 'going equipped' was on my way to Docklands at an ungodly hour to fix a sick mux, so a reasonable explanation for tools and test kit.