I was cleaning out my attic last weekend and found a box of old cold blueing kits from the 80s. Back then, we used those kits all the time for touch-ups on customer guns. Nowadays, most shops have hot tanks or send out for professional finishes. This find had me recall how much simpler some jobs were, but also how much better the results are now. Still, keeping a cold blue pen around isn't a bad idea for quick fixes.
They hold small parts in place without clutter.
I used to lose small parts all the time when cleaning multiple firearms. Now I drop each gun's pieces into separate muffin cups, and nothing gets mixed up. Why do so many smiths stick with expensive organizers when kitchen stuff works better?