Tbh, the "just shake it" advice misses the point with shimmer inks. The guy at the show told me he adds one tiny drop of dish soap to a whole bottle. It breaks the surface tension so the glitter stays mixed in the feed way better. It's a game changer for my cheaper pens that always clogged before.
Shaking a pen is just basic maintenance, not some magic trick. It gets ink flowing in old ballpoints, that's it. People act like it's a life hack for perfect writing.