Aye bought and inserted several colored sets of these markers into our new anchor chain a year or two ago.
Since then, the only time I've taken notice of them is when they're laying around on my deck after weighing anchor.
Personally, I do not think they're worth the effort.
But if you're really hard set on getting some of these hard to come by anchor chain marker inserts - I'll gladly sell you the rest of our's, for half price, plus shipping. But please hurry - I'm loosing them pretty quickly and they'll all be gone before the end of the season.