Nice find, Mark_F. I had an idea to wear the Ritter PSK sparkler as well (it's very lightweight), but figured it will be redundant having the knife there already. Also the wheel would require some serious protection from the skin moisture and abrasion to be readily available for work, but that's an additional weight and bulk. I do have several of these aluminum capsules of various shapes and sizes, but I'm attaching them to my belt-to-pocket lanyard system only, as the coming day plans dictate. I did try them on the neck a while ago - too annoying against the chest and skin for me to EDC. Besides, it's frankly a dead weight (you cannot use it for anything else). My new necklace is riding very well so far, so perfectly unnoticeable that I ended up in the shower wearing it a couple of times (easily dried it with the hair drier, but it's better to avoid doing that, I think, as the ferro-rod metal is quite porous). The weight is the king here for me. Although, I saw smaller rods on eBay (like 1/8" diameter), just have doubts I can affix one to the necklace in the same bulletproof way as the 1/4" one, or use such a small rod without a handle or lanyard.

By the way, you can easily improve that little spark wheel handling by attaching a lanyard to its end (possibly wrapping it around the entire handle length as well, but not necessarily), just experiment with its length to match your palm's size. I've found that stretching it tight between pinky and the handle adds quite a good additional grip to any short handle (another option is a grippy knot on the lanyard's end, shorter length, but bulkier overall).