One is never enough; at least for my own making! Sets are made up of typically 2 or 4 pieces of stitch markers. Some sets include all hexagon ring markers, while others are combinations of both hexagon and removable clasps.
Keep in mind, I am mindful when creating these for what will go best with each item. If the charm is a bit larger or heavier - I will almost never offer it on a hexagon. I've learned, through my own making, that lightweight hexagons are best.
Additionally, I trial all charms for the 'snag factor' before using them in a piece. You can be assured that I won't offer something that would annoy me while knitting.