Yeah I've never had a shimmer ink clog a medium or a broad (or an italic) but I've had it clog some but not all of my fine nibs and I'm like "BUT A FLEXY NIB DOES NOT FIT INTO ANY OF THOSE BOXES" (It's not a very wet writer so now I am nervous!)

Well, they can be cleaned if the worst happens so maybe with a try? (lol, and this is exactly the answer you predicted…)