Like little plastic safety pins, these locking stitch markers stay put - in laceweight through super bulky, knitting or crocheting. I also use them to attach little notes-to-self on my stash as well as on projects in progress. I use them to corral other styles of markers, attach needle-threaders to my scissor-lanyard, and "baste" motifs together before sewing. They have no rough edges, sharp points or tiny crevices so they never snag.
These stitch markers are very nice as they don't snag, and are brightly colored. Jumbo does mean that they are rather awkward at times, but not horribly. I used them on my first project in the round and was very proud of myself in the process due to these babies.
Didn't think I would be using these so much but I love that you can reposition these on what you are knitting and not have to use a large safety pin (which snags) or a darning needle with waste yarn scraps to mark your place. I use them both as markers on stitches and to mark between stitches. The two colors are nice if you are doing cables throughout - I usually use the one color as the beginning of the cable section and the other color as the end - so I am not getting "knitters confusion" as to where I was or should be going (it happens).